The present study examines perceptions of relationship quality as antecedents of best friendship dissolution. Participants included 230 students in Florida (United States; 54.3% girls; ages = 8-13; 39.6% European American, 27.0% Hispanic American, 21.7% African American, and 2.6% Asian American) and 496 students in Lithuania (49.0% girls; ages = 8-14; 358 boys; nearly all ethnic Lithuanian) attending public schools in Florida (United States) and Lithuania. Reciprocated best friends were identified from friend nominations midway through the school year, at which time each partner described perceptions of social support and negativity in the relationship. Of the 363 reciprocated friend dyads, 26.2% (n = 95) were no longer friends 1-3 months later. Dyadic analyses were conducted with initial perceived friend negativity and initial perceived friend social support as predictors of subsequent friendship stability. When considered separately, perceived social support predicted self- and partner reports of friendship stability and perceived negativity predicted self- (but not partner) reports of friendship stability. In each case, lower initial social support and higher initial negativity predicted a greater incidence of friendship dissolution. When considered together, initial perceptions of social support predicted self- and partner reports of friendship dissolution, but perceptions of negativity predicted neither. The findings are consistent with those from married couples, which indicate that the absence of positive interactions is a stronger predictor of relationship instability than the presence of negative interactions. (PsycInfo Database Record (c) 2024 APA, all rights reserved).