PURPOSE: To examine the effects Of cigarette smoking and smoking cessation on the risk of hip fracture in women. PATIENTS AND METHODS: We studied 116,229 female nurses, 34 to 59 years of age at baseline in 1980, who were followed for up to 12 years. Smoking habits and the occurrence of incident hip fractures (n = 377) due to low or moderate trauma were self- reported on biennial mailed questionnaires. RESULTS: Compared with women who had never smoked, the age-adjusted relative risk (RR) of hip fracture among current smokers was 1.3 (95% confidence interval [CI] 1.0 to 1.7). The risk of hip fracture increased linearly (P = 0.09) with greater cigarette consumption (RR = 1.6, 95% CI 1.1 to 2.3 for 25 or more cigarettes per day). These associations were somewhat reduced by adjusting for other risk factors for osteoporosis (menopausal status, use of postmenopausal estrogen, physical activity, and intakes of calcium, alcohol, and caffeine): RR = 1.2, 95% CI 0.8 to 1.3 for all current smokers; RR = 1.4, 95% CI 0.9 to 2.1 for 25 or more cigarettes per day. Relative risks were further reduced when body mass index was added to the model. There was no apparent benefit from quitting smoking until 10 years after cessation. After 10 years, former smokers had a reduced risk of hip fracture (adjusted RR = 0.7, 95% CI 0.5 to 0.9) compared with current smokers. CONCLUSION: Smokers are at increased risk of hip fracture and their risk rises with greater cigarette consumption. Risk declines among former smokers, but the benefit is not observed until 10 years after cessation. Both the increased risk among current smokers and the decline in risk after smoking cessation are in part accounted for by differences in body weight.