Scaphoid fractures predominantly affect young men, in whom the UK smoking prevalence approaches 40%. We examined the association between smoking and failure of non-vascularized bone grafting and screw fixation for scaphoid non-union and delayed union in a retrospective cohort study. Adequate follow-up was obtained in 64 of 87 patients treated (74%). Union was defined as the presence of trabecular continuity on at least two films from a four-view radiographic series. Union was achieved in 47 of 64 cases. Seventeen were smokers. Thirteen of the 17 patients with non-union were smokers (relative risk 3.7; 95% CI: 1.3-10.1, p=0.005). Proximal pole fractures, long injury-grafting interval and non-compliance were not more frequent in smokers than non-smokers. Smoking is strongly associated with failure of union after screw fixation and non-vascularized bone grafting of the scaphoid. Smokers should be advised to avoid smoking pre-operatively and during the healing period.