Hereditary factors play a fundamental role in the pathogenesis of breast cancer (BC). Approximately 15-20% of all BCs have been reported to show familial clustering. In spite of the recent demonstration and chromosomal localization of BC predisposing genes, clinical clues and careful inspection of pedigree still remain major instruments in HBC diagnosis. The aim of the present study was to develop minimum operational criteria for the selection of family groups at high risk of developing BC. Following a stepwise procedure, families were stratified into four clusters with increasing probability of genetic involvement. So far, 317 BC-prone families have been identified and distributed in the four groups, and 151 high risk women underwent our clinical and mammographic surveillance program. Among these, after a mean follow-up of 24 months, six BCs and one OC were diagnosed (one BC and one OC occurred in the same woman) and one 'interval' BC was observed. Since the prevalence rate so far detected is dramatically higher than that seen at the first round of Italian population-screening programs, our preliminary data support the usefulness of the proposed procedure in selecting high risk individuals.