Gender differences in reported family cancer history could reduce the effectiveness of genetic screening for cancer risk.,We randomized 6 schools to teach ninth graders about health genealogy through workshops or offered a delayed intervention. We assessed the effect of the intervention on reported family history of various cancers along with gender and side of the family from which cancer was reported.,Girls reported more breast cancer in the family. Both sexes reported more maternal relatives with breast cancer. There were no treatment group effects.,There are gender differences in reported family history of breast cancer.