Background Rugby union has a high rate of injury. The increased use of protective equipment may help mitigate these injuries. This study investigated the injury prevention effectiveness of the protective equipment used in rugby union. Methods A cohort of 304 rugby players in Dunedin, New Zealand was followed weekly during the 1993 club season to assess protective equipment use, participation in rugby, and injury outcomes. Generalized Poisson regression was used to model the rate of injury while adjusting for covariates such as level of competition, playing position, and injury history. Results The use of mouthguards appeared to lower the risk of orofacial injury [rate ratio (RR) = 0.56, 95% confidence interval (CI): 0.07-4.63], and padded headgear tended to prevent damage to the scalp and ears (RR = 0.59, 95% CI: 0.19-1.86). Support sleeves tended to reduce the risk of sprains and strains (RR = 0.58, 95% CI: 0.26-1.27). The risk of concussion was not lessened by the use of padded headgear (RR = 1.13, 95% CI: 0.40-3.16) or mouthguards (RR = 1.62, 95% CI: 0.51-5.11). There was no evidence of protective effects for any other equipment item (taping, shinguards, and grease). Conclusions The protective equipment used in rugby union has limited effectiveness in preventing injuries. The results are supportive, however, of a role for mouthguards and padded headgear in preventing orofacial and scalp injuries, respectively, and for support sleeves in preventing sprains and strains.