Breast cancer can be caused by germline mutations in several genes that are responsible for different hereditary cancer syndromes. Some of the genes causing the Fanconi anemia (FA) syndrome, such as BRCA2, BRIP1, PALB2, and RAD51C, are associated with high or moderate risk of developing breast cancer. Very recently, SLX4 has been established as a new FA gene raising the question of its implication in breast cancer risk. This study aimed at answering this question sequencing the entire coding region of SLX4 in 526 familial breast cancer cases from Italy. We found 81 different germline variants and none of these were clearly pathogenic. The statistical power of our sample size allows concluding that in Italy the frequency of carriers of truncating mutations of SLX4 may not exceed 0.6%. Our results indicate that testing for SLX4 germline mutations is unlikely to be relevant for the identification of individuals at risk of breast cancer, at least in the Italian population.