Objective: Mixed martial arts (MMA) is an increasingly popular combative sport involving aggressive techniques that present substantial injury risk. We examined the incidence and types of injuries sustained in MMA fights and compared this with injuries sustained in boxing matches. Design: Consecutive Case Series. Setting: We used data from post-fight medical examinations on all bouts in Edmonton, Canada, between 2000 and 2013. Participants: The participants were 1181 MMA competitors and 550 boxers. Main Outcome Measures: The attending physician conducted a mandatory post-fight examination of all fighters and documented the nature of injuries sustained. Results: Boxers were significantly more likely not to experience injury (49.8% vs 59.4%, P < 0.001), whereas MMA fighters were significantly more likely to experience 1 injury (typically contusion/bruising, P < 0.001). Boxers were more likely to experience loss of consciousness (7.1% vs 4.2%, P = 0.01) and serious eye injury (1.1% vs 0.3%, P = 0.02). Conclusions: The overall injury incidence in MMA competitors appears slightly higher than for boxers, but MMA fighters experience more minor contusion/bruising injuries. Boxers are more likely to experience serious injury such as concussion/head trauma involving loss of consciousness or eye injury such as retinal detachment.