This article provides a critical review of various methods for assessing sexual orientation in previous lesbian/gay/bisexual studies. A content analysis of 144 lesbian/gay/bisexual studies published in the Journal of Homosexuality (Volumes 1 to 24; 1974-93) was conducted by two independent reviewers. Findings suggest that women and bisexuals were underrepresented, and, in about one third of the studies, participants' sexual orientations were assumed rather than assessed. Five methods for the assessment of sexual orientation were identified, with self-identification (as heterosexual/homosexual/bisexual/lesbian/gay) the most typical. Each assessment method was critically examined and a 2-by-2 multidimensional assessment model was suggested for use in lesbian/gay/bisexual studies.