This study reports a randomized clinical trial evaluating the efficacy of an intervention to prepare individuals to communicate BRCA1/BRCA2 results to family members. Women aged 18 years and older, who had genetic testing, and who had adult first-degree relatives, were randomly assigned to a communication skills-building intervention or a wellness control session. Primary outcomes were the percentage of probands sharing test results, and the level of distress associated with sharing. The ability of the theory of planned behavior variables to predict the outcomes was explored. Four hundred twenty-two women were enrolled in the study, 219 (intervention) and 203 (control). Data from 137 in the intervention group and 112 in the control group were analyzed. Two hundred forty-nine probands shared test results with 838 relatives (80.1 %). There were no significant differences between study groups in the primary outcomes. Combining data from both arms revealed that perceived control and specific social influence were associated with sharing. Probands were more likely to share genetic test results with their children, female relatives and relatives who they perceived had a favorable opinion about learning the results. The communication skills intervention did not impact sharing of test results. The proband's perception of her relative's opinion of genetic testing and her sense of control in relaying this information influenced sharing. Communication of test results is selective, with male relatives and parents less likely to be informed. Prevalent psychosocial factors play a role in the communication of genetic test results within families.