Following a jury trial, appellant was convicted of unlawful possession of heroin with intent to distribute, in violation of D.C.Code § 48-904.01(a)(l) (2001), and sentenced to 144 months (twelve years) in prison followed by five years of supervised release. On direct appeal, this court affirmed his conviction by unpublished Memorandum Opinion and Judgment on April 21, 2005. Appellant subsequently filed a motion to reduce sentence pursuant to Super. Ct.Crim. R. 35, which the trial court denied. On appeal, he argues that the trial court abused its discretion in denying his motion and, for the first time on appeal, contends that his sentence violated the Eighth Amendment in that it was disproportionate to the crime committed. We affirm.
We review the denial of a motion for the reduction in sentence for an abuse of discretion. See Walden v. United States, 366 A.2d 1075, 1076-77 (D.C.1976). In so doing, “[t]his court has long refused, in considering ... an appeal of a post-trial decision on sentence reduction, to review ... sentences which are within statutory limits, on the ground that such sentences are too severe.” Crawford v. United States, 628 A.2d, 1002, 1003-1004 (D.C.1993) (citations and internal quotation marks omitted). Indeed, “[gjenerally, sentences within statutory limits are unre-viewable aside from constitutional considerations.” Id. at 1003-1004 (citation and internal quotation marks omitted).
Here, appellant’s sentence fell well within the thirty-year statutory maximum for the offense of which he was convicted. D.C.Code § 48-904.01(a)(2)(A) (2001). In his motion to reduce sentence appellant’s primary argument was that “[h]ad Mr. Cook received a ‘guideline sentence’ under the current sentencing guidelines for the same offense, his sentence would have been significantly less than his current sentence.” However, the Superior Court Voluntary Sentencing Guidelines were not in effect at the time of sentencing and, regardless, being voluntary would not have compelled the trial court to impose a lesser sentence. Given our “very limited” standard of review on these issues, we are not persuaded that the trial court abused its discretion in denying the motion. See Walden, supra, 366 A.2d at 1077.
Turning to appellant’s constitutional argument, we note that “[w]here a defendant has failed to raise an available challenge to his conviction on direct appeal, he may not raise that issue on collateral attack unless he shows both cause for his failure to do so and prejudice as a result of his failure.”1 See Head v. United *508States, 489 A.2d 450, 451 (D.C.1985) (citations omitted). Here, appellant failed to raise his Eighth Amendment claim on direct appeal, instead raising it for the first time as part of this appeal. In so doing he proffers no cause for this failure. Thus, we “need not decide whether he suffered prejudice or even if the trial court was in error.” See id. at 451 n. 5 (citation omitted). Accordingly, because appellant has failed to demonstrate the requisite cause for his failure to have raised the issue on direct appeal, “his contention here is foreclosed.” See id. at 451.
Even if we were to consider appellant’s claim on the merits, we are not convinced that appellant’s sentence was so disproportionate as to contravene the Cruel and Unusual Punishment Clause of the Eighth Amendment.2 We are mindful that following the Supreme Court’s decisions in Harmelin v. Michigan, 501 U.S. 957, 111 S.Ct. 2680, 115 L.Ed.2d 836 (1991), and Ewing v. California, 538 U.S. 11, 123 S.Ct. 1179, 155 L.Ed.2d 108 (2003), the standard for claims of disproportionate sentences has been narrowed3 and, at a minimum, now appears to require a showing that a sentence is “grossly disproportionate” to the crime. See Crawford, supra, 628 A.2d at 1003; Moore, supra, note 2, 608 A.2d at 145 n. 3. Under this standard, we are not convinced that appellant’s sentence was “grossly disproportionate” to the crime. It was well within the statutory maximum and, as the government notes in its brief, there were a number of aggravating circumstances affecting the length of sentence imposed by the trial court. See Hutto v. Davis, 454 U.S. 370, 102 S.Ct. 703, 70 L.Ed.2d 556 (1982) (upholding a sentence of forty years imprisonment for possession with intent to distribute nine ounces of marijuana). Accordingly, the judgment on appeal herein is hereby affirmed.
So ordered.
. In the context of a Rule 35(a) motion to correct an illegal sentence, we have held that, even where the appellant has failed to raise the issue on direct appeal, a challenge may be brought "without regard to cause and prejudice requirements.” Brown v. United States, 795 A.2d 56, 63 (D.C.2002); see also (Timothy) Robinson v. United States, 454 A.2d 810, 813 ("Where the sentence is ‘illegal’ in the sense that the court goes beyond its authority by acting without jurisdiction or imposing a sentence in excess of the statutory maximum provided, then such sentence — because of the gravity of the error, the unqualified deprivation of one’s liberty — may be challenged at any time.”). As the same concerns informing our decisions pertaining to Rule 35(a) do not apply to Rule 35(b) motions, see Walden, supra, 366 A.2d at 1077 (“A motion for reduction in sentence is basically a 'plea for leniency.’ ” (citation omitted)), we conclude that *508cause and prejudice requirements remain applicable here.
. We recognize that appellant relies on the concurring opinion in Moore v. United States, 608 A.2d 144, 147 (1992) (Schwelb, J., concurring), in advancing his Eighth Amendment argument. However, under the circumstances of this case we do not reach the merits of this argument because of the procedural barriers present here.
. Prior to Harmelin, the Supreme Court set forth three factors relevant to determining whether a sentence was disproportionate to the crime committed: "(i) the gravity of the offense and the harshness of the penalty; (ii) the sentences imposed on other criminals in the same jurisdiction; and (iii) the sentences imposed for commission of the same crime in other jurisdictions.” Solem v. Helm, 463 U.S. 277, 292, 103 S.Ct. 3001, 77 L.Ed.2d 637 (1983). In Harmelin, Justice Scalia, joined by Chief Justice Rehnquist, concluded that Solem "was simply wrong; the Eighth Amendment contains no proportionality guarantee.” Harmelin, supra, 501 U.S. at 965, 111 S.Ct. 2680 (opinion of Scalia, J.). In a concurring opinion, Justice Kennedy, joined-by Justices O’Connor and Souter, wrote that the court’s decisions on the issue recognized only "a narrow proportionality rule” that does not require "strict proportionality between crime and sentence.” Id. at 997, 1001, 111 S.Ct. 2680 (Kennedy, J., concurring in part and concurring in the judgment). With respect to the Solem factors, Justice Kennedy stated that the latter two factors were Only appropriate "in the rare case in which a threshold comparison of the crime committed and the sentence imposed leads to an inference of gross disproportionality.” Id. at 1005, 111 S.Ct. 2680.