In a survey of instructors of human sexuality courses at 58 US universities and colleges, for 51 institutions the female/male ratio of enrolled undergraduate students ranged from 2/1 to 38/1, and typically 3/1 to 6/1. Most courses were offered in departments of psychology or health, which usually have high F/M ratios for majors. However, the high F/M ratios in sexuality courses could not be explained entirely by departmental or institutional F/M ratios, and were not related to the size of the course, the gender of the instructor, or the geographical area of the country. It is concluded that men are much less likely than women to enrol in a college sexuality course. Many instructors expressed concern about the high F/M ratios and some attributed it to stereotypes about masculinity. Research indicates that masculine ideologies result in many boys having a negative attitude about sex education. Many university men believe that they already know enough about sex, but there was some evidence that men were more likely to enrol when courses were offered on-line, allowing for some degree of anonymity and privacy.