A statewide cohort study on the occurrence of second primary neoplasms was conducted among 9678 women first diagnosed with breast cancer in Saarland, Germany between 1968 and 1987. A total number of 409 second primary neoplasms was observed compared to 328 cases that would have been expected based on the incidence rates of the general population (standardised incidence ratio, SIR = 1.25). This elevation in incidence of second neoplasms was primarily due to increased occurrence of cancer of the opposite breast (SIR = 2.48), which was most pronounced for patients below the age of 50 (SIR = 4.20) and within the first 5 years after diagnosis (SIR = 2.91). There was a moderate elevation in incidence of malignant tumours of the ovaries (SIR = 1.46), while the incidence of most other malignancies was lower than in the general population. Our results, which are in agreement with previous findings from Northern Europe, the U.S.A. and Japan provide valuable background information for aetiological research, as well as for surveillance of breast cancer patients.