Objective: To investigate the risk factors of bone metastases in breast carcinoma. Methods: By cross sectional study, the data of 225 breast cancer patients who were inpatients in four hospitals in Hangzhou were analyzed. All patients underwent total body bone scan with single photon emission computed tomography (SPECT) at least once during 1995 to 2000. Results: All patients were followed-up to 294 months after operation, bone metastases were found in 113 cases, suspected bone metastases 3 cases, with a bone metastases rate of 50.9% (113/222). Multivariate analysis by Coxs proportional hazards regression model showed that there were four risk factors of bone metastases in breast cancer: (1) clinical stage, I(IV stages with a hazard ratio of bone metastases of 1.945, 95% confidence interval 1.396(2.710; (2) number of invaded axillary lymph nodes, with a hazard ratio of 1.039, 95% confidence interval 1.0142(1.068; (3) skeletal complications (yes vs. no), with a hazard ratio of bone metastases of 1.722, 95% confidence interval 1.060(2.796; (4) age at the time of surgery or diagnosis, with a hazard ratio of 2.048, 95% confidence interval 1.123(3.876 for patients of age 40(50 y versus patients bellow 40 y of age and 2.837, 95% confidence interval 1.473(5.465 for patients of age above 50 y versus patients of ages between 40 and 50. Kaplan-Meier curves showed that for patients with more than 5 invasive axillary lymph nodes, compared with those with 1(5, the bone metastasis rates increased significantly ((2 =6.3319, P=0.012). Conclusion: The clinical stage, number of metastatic axillary lymph nodes, age at the time of operation and skeletal complications are essential risk factors of bone metastases.