The extent and experiences of youths' caretaking of their adolescent sisters' children have been assessed in two longitudinal studies. The first study examines the caretaking patterns of 132 Latino and African American youth during middle and late adolescence. The second study involves 110 Latino youth whose teenage sister has recently given birth. Youth are studied at 6 weeks and 6 months postpartum. In both studies, girls provide more hours of care than boys, and in Study 1, girls' hours of care significantly increase with age whereas boys' hours of caretaking decrease. Girls provide more care when their sisters are older and when their mothers provide many hours of care, whereas boys provide less care when their mothers provide more care and when they have many siblings. Results of both studies reveal age, gender, and across-time differences in the extent of care, type of caretaking activities, and experiences in providing care. (Contains 5 tables and 3 figures.)