In families where the hereditary transmission of breast (BC) and/or ovarian cancer (OC) risk is suspected, BRCA1/2 testing is indicated. However, while not all BRCA carriers develop cancer, cases of sporadic BC/OC among non-carriers members of BRCA+ families may occur. No clear data are available so far about the expected frequency of these cases. One 2005 work by Allweis et al. reported a frequency of 0.75% sporadic cancers in a cohort of Ashkenazi BC patients tested for BRCA1/2. Here we report a case series of sporadic BC/OC in families with BRCA-associated HBOC syndrome. Subjects accessing to Hereditary and Familial Tumours Services (HFTS) at Vito Fazzi Hospital in Lecce were considered. Families were classified based on Modena criteria. We identified the HBC/HBOC families in which a 1st-degree non-carrier relative of at least one BC and/or OC affected BRCA carrier also developed cancer. All subjects provided consent to genetic testing and research data collection. Between January 2014-April 2016, 424 subjects from 314 families accessed to HFTS, for a total of 608 counseling visits. Of 424, 271 (63.9%) were considered to be eligible for BRCA1/2 testing, finding 98 BRCA1/2 wild type subjects, and 66 BRCA1/2 mutations carriers (plus 5 subjects with VUS). Of 314 families considered, 87 (27,6%) were classified as HBC/HBOC. Four families (4/87, 4.6%) were identified in which one cancer affected member was non-carrier of the familial BRCA mutation. In particular, these were three BC cases of a paternal aunt, sister and daughter, respectively, of affected BRCA1 mutation carriers; and one case of high-grade serous OC developed at age 57 in a non-carrier younger sister of a BRCA1 carrier patient who had developed high-grade serous OC at age 61. As particularly impressive in the OC case, for the three BC cases we observed similarities in terms of clinical and pathologic characteristics of cancers between carriers and non carriers. Relatives of BRCA carriers who result non-carrier are normally counseled that their BC/OC risk is the same as for the general population, and so are the prevention programs. However, as we report here, sporadic BC/OC may occur in 4.6% cases, most probably due to the same environmental factors shared, or other unconventional triggers (stress/lifestyle-related, or pollution-driven). However, further studies should be conducted to determine prevalence and risk of sporadic cancer, that may help guide counseling.