The purpose of this study, which involved 276 patients, was to report the importance of Propionibacterium acnes in shoulder infections. The proportion of patients with shoulder infection who had infection due to P. acnes was significantly greater than the proportion of patients with lower limb infection who had infection due to P. acnes (9 of 16 patients vs. 1 of 233 patients; P < .001). This bacterium requires a prolonged incubation period and should not be considered to be a contaminant.