This study examines whether the relation between acute cannabis use and syringe sharing during single injection days is similar among regular and nonregular users, participating in a cohort study of injection drug users in Montréal, Canada. 236 (36.6%) subjects were classified as regular cannabis users (RCUs), 227 (35.2%) as nonregular cannabis users (NRCUs), and 181 (28.1%) were abstinent. Cannabis use during a single injection day was associated with a fivefold increased risk of sharing (OR 4.92; 1.83-13.22) in NRCUs compared to RCUs. Our results indicate that cannabis use history should be considered when evaluating its potential effect on risk-taking behaviors.