This is the first report of a full genome scan of sexual orientation in men. A sample of 456 individuals from 146 families with two or more gay brothers was genotyped with 403 microsatellite markers at 10-cM intervals. Given that previously reported evidence of maternal loading of transmission of sexual orientation could indicate epigenetic factors acting on autosomal genes, maximum likelihood estimations (mlod) scores were calculated separated for maternal, paternal, and combined transmission. The highest mlod score was 3.45 at a position near D7S798 in 7q36 with approximately equivalent maternal and paternal contributions. The second highest mlod score of 1.96 was located near D8S505 in 8p12, again with equal maternal and paternal contributions. A maternal origin effect was found near marker D10S217 in 10q26, with a mlod score of 1.81 for maternal meioses and no paternal contribution. We did not find linkage to Xq28 in the full sample, but given the previously reported evidence of linkage in this region, we conducted supplemental analyses to clarify these findings. First, we re-analyzed our previously reported data and found a mlod of 6.47. We then re-analyzed our current data, after limiting the sample to those families previously reported, and found a mlod of 1.99. These Xq28 findings are discussed in detail. The results of this first genome screen for normal variation in the behavioral trait of sexual orientation in males should encourage efforts to replicate these findings in new samples with denser linkage maps in the suggested regions.