Family history is an important breast cancer risk factor and is a common reason for referral to specialist breast clinics for consideration of breast screening. The aims of this study were to determine cancer detection rates and prognostic features of breast cancers identified in women aged less than 50 years at increased risk of breast cancer who attend a Family History Breast Screening Clinic (FHC). Between January 1988 and December 1995, 1371 asymptomatic women aged less than 50 years underwent annual clinical breast examination and biennial mammography due to a family history of breast cancer. A total of 29 cancers (23 invasive and 6 in situ) were detected or presented as interval cancer during a mean follow-up of 22 months (range 0-96 months). This gave a relative risk for invasive breast cancer in this high-risk group of 5 when compared with an age-matched female population in the U.K. The cancer screening detection rates were similar to those of women aged 50 years or over undergoing population screening in the NHS Breast Screening Programme (NHSBSP)--FHC prevalent screen 8 per 1000 screening visits versus NHSBSP 6.5 per 1000, FHC incident screen 3.3 per 1000 screening visits versus NHSBSP 3.8 per 1000. A higher proportion of in situ cancers were detected in the FHC screened group compared with cancers identified in symptomatic patients from an age-matched risk group (21% versus 4%). No differences were demonstrated for invasive tumour size, grade or lymph node stage between symptomatic and screened women. The early results of this study suggests that young women at risk of breast cancer due to a family history may benefit from regular breast screening due to the early detection of in situ lesions.