Using a sample of 193 Mexican American adolescents (M age at Wave 1 = 14 years) and three waves of data over 2 years, this study longitudinally examined the effects of parent–youth acculturation differences, relative to no differences, on parent–adolescent relationship quality and youth problem behavior. We examined parent–youth differences in overall acculturation, Mexican acculturation, and American acculturation. We differentiated between cases in which the adolescent was more acculturated than the parent and cases in which the parent was more acculturated than the adolescent. Adolescents were more commonly similar to their parents than different. Where differences existed, adolescents were not uniformly more American than their parents, no type of difference was associated with parent–adolescent relationship quality, and no type of difference in overall acculturation was associated with youth problem behavior. One type of difference by dimension (adolescent had less Mexican acculturation than mother) was associated with less risk of problem behavior.