We report on 156 consecutive cases of in situ ductal carcinoma (DCIS) of the breast observed from 1968 to 1988. The relative frequency of DCIS was much higher in screened, with respect to self-referred, women and a significant association of DCIS with younger age was observed. The combined use of mammography and physical examination identified 138 of 156 total DCIS cases as suspicious. Mammography, physical examination or cytology (of nipple discharge or needle aspirate) were the only tests to provide suspicious evidence in 35, 22 and four cases respectively. DCIS was a relatively unexpected surgical finding in 13 apparently benign cases. Different surgical options were recorded in the study period but a temporal trend in favour of conservative surgery was evident. Subsequent ipsilateral or contralateral breast cancer was recorded in seven and six cases respectively. Death from breast cancer occurred in five cases, all of whom had contralateral or subsequent ipsilateral infiltrating cancer. This figure confirms the high curability of DCIS if local control is achieved.