The Humberside Breast Screening Service completed 1 year of screening by October 1990; 16,534 women were invited of whom 12,832 (77.6 per cent) attended. A group of 644 women (5.0 per cent) were called for further assessment and of these 134 underwent 135 primary surgical procedures. After assessment 25 were shown before operation to have cancer. One hundred and nine women had suspicious lesions and proceeded to surgical biopsy; 50 lesions proved malignant (benign: malignant biopsy ratio 1.2:1). The 75 malignant lesions represented a prevalence of 5.8 per 1000 of the screened population. Invasive cancer > 1 cm in diameter formed almost half of the malignant lesions. This service has cost 32 pounds per woman screened or 5533 pounds per cancer detected. The results are comparable to those of previous studies and suggest that a mammographic screening service can be successfully provided in a district hospital setting.