PURPOSE: Androgen deprivation therapy increases the risk of osteoporosis related fractures. This issue is of increasing importance in men with prostate cancer as increasingly more undergo androgen deprivation therapy and therapy is administered sooner following diagnosis. Data directly addressing the long-term fracture risk in men diagnosed with prostate cancer are limited. MATERIALS AND METHODS: Using population based registries in Sweden we studied the incidence of hip fractures in 17,731 men diagnosed with prostate cancer from 1964 to 1996 who were treated with bilateral orchiectomy within 6 months of diagnosis. The fracture incidence was compared to the incidence in 43,230 men diagnosed with prostate cancer but not treated with orchiectomy and in 362,354 of similar age who were randomly selected from the general population. RESULTS: Men treated with orchiectomy were at increased risk for hip fracture. The estimated relative risk comparing men who underwent orchiectomy to population controls was 2.11 (95% CI 1.94 to 2.29) for femoral neck fractures and 2.16 (95% CI 1.97 to 2.36) for intertrochanter fractures. An increased risk of hip fracture was observed as early as 6 months after orchiectomy and the relative risk remained fairly constant up to 15 years following orchiectomy. CONCLUSIONS: Hip fracture risk increases almost immediately following orchiectomy and the excess risk persists for at least 15 years. This side effect should be considered when assessing the merits of androgen deprivation therapy, particularly in symptom-free men diagnosed with localized prostate cancer. Measures to prevent osteoporosis should be considered in men undergoing androgen deprivation therapy.