The purpose of this study is to determine the prevalence of PALB2 mutations among breast cancer families from the United States. The PALB2 gene was screened for mutations in 90 familial breast cancer patients from the Creighton University Breast Cancer Family Registry. These patients had previously tested negative for mutations in BRCA1 and BRCA2. Two of 90 breast cancer patients (2.2 %) were found to carry a truncating mutation in PALB2 (c.2411_2412delCT and c.2053delC). Both probands were diagnosed with breast cancer before age 35 and each had three relatives with breast cancer. Mutations in PALB2 are less common than BRCA1 and BRCA2 in familial breast cancer patients. However, testing for PALB2 mutations is a useful adjunct for patients undergoing testing for BRCA1 and BRCA2.