We examined the association of dyadic-level factors with syringe sharing among people who inject drugs (PWID) in Kerman, Iran. In a cross-sectional study, we collected data on 329 drug-injecting dyads by individual face-to-face interviews. An injecting dyad was defined as 2 PWID who knew each other and injected drugs together during the last 6 months. If they reported at least 1 occasion of syringe sharing, the dyad was considered high-risk. Dyadic-level factors associated with syringe sharing were assessed using cross-classified multilevel logistic regression. The rate of syringe sharing was significantly higher for dyads who were more intimate (adjusted odds ratio [AOR] 4.5, CI 95%, 2.3-8.6), who had instrumental support (AOR 2.1, 95% CI 1.1-4.5), and who pooled money for drugs (AOR 4.1, 95% CI 2.0-8.3). The rate was lower in same-sex dyads (AOR 0.4, 95% CI 0.2-0.9) and in dyads who shared health information (AOR 0.5, 95% CI 0.2-0.9). Findings highlight close-peer influences on syringe-sharing behavior.