Study objective: To describe and explain variation among general practices in the uptake of screening for breast cancer. Design: Analysis of the variation in uptake of screening by general practice. Uptake rates are calculated and related to a social deprivation score created for each practice, and to the presence of at least one female general practitioner. Setting: South Lancashire Health Authority, England. Patients: All women aged 50–64 y registered with Lancashire Family Health Services Authority and resident in South Lancashire in 1988–1995. Main results: Variation in the uptake of screening for breast cancer during Round 1 of the national programme is explained partly by a deprivation score for each practice and by the presence of at least one female general practitioner. In Round 2 the deprivation index continues to explain variation, but the effect of a female GP has diminished. The number of hours worked by practice nurses has no effect on uptake of breast screening. Conclusions: Variation in the uptake of breast cancer screening is closely related to social deprivation. Results suggest that the presence of a female general practitioner has a beneficial effect on uptake.