The early and accurate diagnosis of breast cancer is of paramount importance in the symptomatic patient. In this study, the sensitivity and false negative rates of clinical assessment and community mammographic imaging are measured and compared. One hundred and sixty-nine histologically proven breast cancers, derived from one surgeon's practice, were clinically assessed. Of these, 108 were additionally assessed by mammography. Eighty-seven per cent of the patients with breast cancer presented with a lump. In 82.8% of cases the patient or her partner found the lump, while 12.3% of lumps were found by the family practitioner. The false negative rate for clinical diagnosis was 19%, and for mammographic diagnosis it was 29%. Premenopausal mammographic diagnosis had a significantly higher false negative rate (54%) than postmenopausal diagnosis (14%). Mammographic examination had a particularly high false negative rate (65%) when cancer was thought clinically to be of "low index of suspicion". The clinical evaluation of and the indications for biopsy of the symptomatic breast remain the essential step in the diagnosis of breast cancer.