The distribution of germline mutations in breast/ovarian cancer (BC/OC) families varies among different populations. In the Chilean population, there are only two reports of mutation analysis of , and these included a low number of BC and/or OC patients. Moreover, the prevalence of genomic rearrangements in Chilean and in other South American populations is unknown. In this article, we present the mutation-detection data corresponding to a set of 326 high-risk families analyzed by conformation-sensitive gel electrophoresis and heteroduplex analysis. To determine the contribution of LGRs in Chilean BC patients, we analyzed 56 high-risk subjects with no pathogenic point mutations. Germline / point mutations were found in 23 (7.1%) of the 326 Chilean families. Families which had at least three BC and/or OC cases showed the highest frequency of mutations (15.9%). We identified 14 point pathogenic mutations. Three recurrent mutations in (c.187_188delAG, c.2605_2606delTT, and c.3450_3453delCAAG) and three in (c.4969_4970insTG, c.5374_5377delTATG, and c.6503_6504delTT) contributed to 63.6 and 66.7% of all the deleterious mutations of each gene, which may reflect the presence of region-specific founder effects. Taken together recurrent point mutations account for 65.2% (15/23) of the (+) families. No large deletions or duplications involving / were identified in a subgroup of 56 index cases negative for point mutations. Our study, which is the largest conducted to date in a South American population, provides a comprehensive analysis on the type and distribution of mutations and allelic variants.