Appeal from an order of the Family Court of Broome County (Ray, J.), entered March 5, 2003, which partially granted petitioner’s application, in a proceeding pursuant to Family Ct Act article 6, to modify a prior order of custody.
*704The parties are the biological parents of a daughter, born in 1998. In November 2000, the parties entered into a stipulation providing for joint legal custody and alternating physical custody, with the child residing with petitioner four days and nights per week and with respondent three days and nights per week. This arrangement continued until September 2002, at which time petitioner commenced the instant modification proceeding seeking sole legal and physical custody of the child. Family Court thereafter issued a temporary order granting petitioner custody of the child and limiting respondent’s visitation. The matter proceeded to a hearing, at the conclusion of which Family Court, inter alia, granted petitioner sole custody of the child and awarded respondent visitation on alternating weekends. This appeal by respondent ensued.
“[W]here, as here, the parties have entered into a voluntary joint custody agreement, such agreement will not be cast aside ‘unless there is a sufficient change in circumstances since the time of the stipulation and unless the modification of the custody agreement is in the best interests of the child[ ]’ ” (Matter of Morin v Stancu, 309 AD2d 1035, 1036 [2003], quoting Matter of Gaudette v Gaudette, 262 AD2d 804, 805 [1999], lv denied 94 NY2d 790 [1999]; see Matter of Crocker v Crocker, 307 AD2d 402 [2003], lv denied 100 NY2d 515 [2003]). Based upon our review of the record as a whole, we are satisfied that petitioner met that burden here. The parties’ respective witnesses portrayed two very different assessments of respondent’s lifestyle, home environment and parenting skills. According to petitioner and his witnesses, respondent places her own needs above those of her daughter, runs what amounts to a flophouse for transient teenagers and ex-boyfriends, lives in absolute squalor in a residence dominated by dog feces and garbage and frequently leaves the child to bathe or play outside unsupervised. Petitioner also testified that the child frequently returned from respondent’s care with various illnesses or infections, including lice, and that respondent failed to give the child prescribed medication. Respondent, on the other hand, testified that she rarely socializes outside her home and stated that, although she occasionally provides shelter for friends for brief periods of time, such individuals are not a daily part of her household. As to the actual condition of her residence, which friends and family members characterized as “normal” and “livable,” respondent noted that she is in the process of remodeling and asserted that while the house may at times appear cluttered, it is not unsafe or unsanitary. Respondent also denied any ongoing medical problems with the child and testified that she bathed the child on a daily basis. In short, Family Court was presented *705with conflicting facts and events which, at the end of the day, distilled to a credibility determination. Family Court, having had the opportunity to hear the witnesses’ testimony firsthand and observe their demeanor, plainly elected to resolve the credibility issues in favor of petitioner and, as its determination in this regard has a sound and substantial basis in the record, we see no reason to disturb it (see Matter of Ebel v Urlich, 273 AD2d 530, 531 [2000]).
To the extent that respondent contends that Family Court erred in failing to appoint a law guardian for the child, “the case law makes clear that, although the appointment of a Law Guardian in a contested custody matter remains ‘the preferred practice,’ such appointment is discretionary, not mandatory” (Matter of Lips v Lips, 284 AD2d 716, 716 [2001], quoting Matter of Davis v Davis, 269 AD2d 82, 85 [2000]). Based upon the particular facts of this case, we perceive no abuse of Family Court’s discretion in this regard. Accordingly, Family Court’s order is in all respects affirmed.
Mugglin and Lahtinen, JJ., concur.