Self-representations play an important role in adolescent development. This study compared self-representations for siblings and explored whether sibling relationship characteristics are associated with similarities or differences in sibling self-concepts. We examined self-representations of 438 adolescent sibling dyads (M age younger sibling = 11.6 years, M age older = 14.3 years), finding that siblings are, on average, similar in their self-representations. This similarity varied, however, depending on sex composition and sibling relationship qualities. Results indicated that sibling modeling, warmth, and conflict were especially influential in predicting sibling resemblance vs. dissimilarity.