Pathogenic germline mutations in and () account for the majority of hereditary breast and/or ovarian cancers worldwide. To refine the spectrum of mutations and to accurately estimate the prevalence of mutation in the Pakistani population, we studied 539 breast cancer patients selected for family history and age of diagnosis.Comprehensive screening for germline mutations was performed using state-of-the-art technologies.A total of 133 deleterious mutations were identified in 539 families (24.7%), comprising 110 in and 23 in . The prevalence of small-range mutations and large genomic rearrangements was 55.4% (36/65) for families with breast and ovarian cancer, 27.4% (67/244) for families with two or more cases of breast cancer, 18.5% (5/27) for families with male breast cancer, and 12.3% (25/203) for families with a single case of early-onset breast cancer. Nine mutations were specific to the Pakistani population. Eighteen mutations in and three in were recurrent and accounted for 68.2% (75/110) and 34.8% (8/23) of all identified mutations in and , respectively. Most of these mutations were exclusive to a specific ethnic group and may result from founder effects.Our findings show that mutations account for one in four cases of hereditary breast/ovarian cancer, one in five cases of male breast cancer, and one in eight cases of early-onset breast cancer in Pakistan. Our study suggests genetic testing of an extended panel of 21 recurrent mutations for appropriately selected patients and their families in Pakistan.