Early diagnosis is a tenet in oncology and should enable early treatment with the expectation of improved outcome. Extent and determinants of patient delay of diagnosis in breast cancer patients and its impact on stage of disease were examined in a population based study among female breast cancer patients in Germany. Two hundred and eighty-seven women, aged 18 to 80 years with newly diagnosed invasive symptomatic breast cancer, were interviewed with respect to the diagnostic process. Patient delay was defined as time from onset of first symptoms to first consultation of a doctor. Median patient delay was 16 days among symptomatic patients. Eighteen per cent of all breast cancer patients waited longer than 3 months before consulting a physician. Long patient delay was associated with old age, history of a benign mastopathy, obesity, and indices of health behaviour such as not knowing a gynaecologist for out-patient care and non-participation in general health screening examinations. A strong association between patient delay and stage at diagnosis was observed for poorly differentiated tumours. These results suggest that at risk groups for delaying consultation can be identified and that a substantial proportion of late stage diagnoses of poorly differentiated breast cancer cases could be avoided if all patients with breast cancer symptoms would present to a doctor within 1 month.