The present study examined whether positive or negative links occur between psychosocial adjustment and sexual activity with four types of partners-romantic partners, friends, acquaintances, and friends with benefits. We examined longitudinal associations and concurrent between-person and within-person associations. A representative sample of 185 participants (93 males, 92 females), their friends, and mothers completed questionnaires when the participants were 2.5, 4, and 5.5 years out of high school. Regardless of the type of partner, more frequent sexual activity relative to the sexual activity of other young adults was associated with more substance use and risky sexual behavior (i.e., between-person effects). Similarly, for all types of nonromantic partners, more frequrent sexual activity relative to one's own typical sexual activity was associated with more substance use and risky sexual behavior (i.e., within-person effects). Differences in frequency of sexual activity with friends and acquaintances were associated with greater internalizing and externalizing symptoms as well as lower self-esteem. Follow-up analyses revealed the associations were particularly strong for friends with benefits. Women's sexual activity frequency with a nonromantic partner was more commonly associated with poorer psychosocial adjustment than such activity by men. More frequent sexual activity with a romantic partner was associated with higher self-esteem and lower internalizing symptoms. Few long-term effects were found for any type of sexual activity. The findings underscore the importance of examining relationship context and illustrate the value of using multiple analytic strategies for identifying the precise nature of associations.