To further characterized the spectrum of TP53 germline mutations in French Canadians, we describe the mutations found in hereditary cancer clinics, investigate breast/ovarian cancer probands from 37 new HBC/HBOC families found negative for BRCA1 and BRCA2 germline mutations, and report on the frequency of mutations found in a targeted screen of 1235 French Canadian breast cancer cases for TP53 mutations found in hereditary cancer families. The gene discussed is TP53; the disease is breast cancer.