The general public as well as the scientific community have use for accurate data on the size(s) of the heterosexual, homosexual, and bisexual populations. Uses include political, legal, medical, and social. The data upon which the typically used figures are dependent have come under scrutiny. This review of studies from the U.S. and elsewhere indicate that it is unreasonable to consider the often-used figure of 10% of the male population as more or less regularly engaging in same-sex activities. The figure is closer to half that. And the figure for the lesbian population is even smaller. Further, routinely exclusive or predominantly exclusive homosexual activities are more common than bisexual activities.