BackgroundSharing of syringes is the leading transmission pathway for hepatitis C (HCV) infections. The extent to which HCV can spread among people who inject drugs (PWID) is largely dependent on syringe-sharing network factors. Our study aims to better understand partnership characteristics and syringe and equipment sharing with those partners, including measures of relationship closeness, sexual activity, and social support, as well as self and partner HCV status to better inform interventions for young urban and suburban PWID.MethodsData are from baseline interviews of a longitudinal network-based study of young (aged 18–30) PWID (egos) and their injection network members (alters) in metropolitan Chicago (n = 276). All participants completed a computer-assisted interviewer-administered questionnaire and an egocentric network survey on injection, sexual, and support networks.ResultsCorrelates of syringe and ancillary equipment sharing were found to be similar. Sharing was more likely to occur in mixed-gender dyads. Participants were more likely to share syringes and equipment with injection partners who lived in the same household, who they saw every day, who they trusted, who they had an intimate relationship with that included condomless sex, and who provided personal support. PWID who had tested HCV negative within the past year were less likely to share syringes with an HCV positive partner compared to those who did not know their status.ConclusionPWID regulate their syringe and other injection equipment sharing to some extent by sharing preferentially with injection partners with whom they have a close personal or intimate relationship, and whose HCV status they are more likely to know. Our findings underscore the need for risk interventions and HCV treatment strategies to consider the social context of syringe and equipment sharing within partnerships.Supplementary InformationThe online version contains supplementary material available at 10.1186/s12889-023-16133-5.