Compared to people who have never engaged in nonsuicidal self-injury (NSSI), people with a history of NSSI report multiple interpersonal problems. Theories propose that these interpersonal difficulties play a role in prompting and maintaining NSSI. The cross-sectional nature of most studies in this area limits our understanding of how day-to-day interpersonal experiences relate to the global interpersonal impairments observed among individuals with NSSI, and vice versa. This study compared young adults with (n = 60) and without (n = 56) recent, repeated NSSI on baseline and daily measures of interpersonal functioning during a 14-day daily diary study. Groups differed in baseline social anxiety, excessive reassurance seeking, and use of support seeking relative to other coping strategies, but did not differ in self-perceived interpersonal competence. In terms of day-to-day functioning, participants with (vs. without) NSSI had significantly less contact with their families and friends, perceived less support following interactions with friends, and were less likely to seek support to cope, regardless of level of negative affect. With the exception of contact with family members, these group differences in daily interpersonal functioning were accounted for by baseline levels of social anxiety and use of support seeking. Contrary to expectations, participants with NSSI had more frequent contact with their romantic partners, did not differ in perceptions of support in romantic relationships, and did not report more intense negative affect following negative interpersonal interactions. This study provides a novel test of recent interpersonal theories of NSSI using daily reports.