The risk of breast cancer and of all malignancies was assessed in first degree relatives of 180 women with breast cancer using a historical cohort study approach. The standardized incidence ratio (SIR) was significantly (p < 0.05) increased for breast cancer in mothers: 1.97 (95% Confidence Interval (CI): 1.27 to 2.91) and in all female first degree relatives: 1.55 (95% CI: 1.08 to 2.15). For breast cancer in sisters it was 1.12 (95% CI: 0.56 to 2.01). For all malignancies the SIR for mothers was 1.12 (95% CI: 0.85 to 1.44), for sisters 1.09 (95% CI: 0.77 to 1.49) and for all female first degree relatives 1.08 (95% CI: 0.89 to 1.32). This study confirms previous investigations showing that breast cancer occurs more frequently in female first degree relatives of women with breast cancer than in the general population.