Five hundred and thirty seven women at risk for breast carcinoma were identified. Family history was detailed and each woman given genetic counselling. Diagnostic examination for breast carcinoma was performed at the major hospitals of Norway, and included physical examination by expert surgeon, mammography and/or ultrasonography, and fine needle aspiration cytology when appropriate. Altogether 8 carcinomas and 5 cases of atypical hyperplasia were found, compared with 1.6 and 0.3 expected, respectively, from population studies. The finding exceeded the expected numbers described by autosomal dominant inheritance. In addition we found one carcinoma in situ. It is concluded that the methods employed are suitable to identify and examine women at risk for breast carcinoma. It is suggested that atypical hyperplasia may be the precancerous lesion, and should be treated as such.