The purpose of this study was to explore heterosexual bias in the diagnosis and treatment of gay males. Two hundred-fifty (134 males and 116 females) mental health professionals from the Division of Psychotherapy (29) of the American Psychological Association participated in the study. Participants were randomly assigned to one of two case history conditions, which presented a 35-year-old male seeking therapy. Both conditions were equivalent with regards to the presenting problem (i.e., diagnostic symptoms) with the exception of his significant other (i.e., gay vs. non-gay condition). Potential bias was measured through a diagnostic rating Likert scale and a treatment plan questionnaire. Other independent variables that could potentially have an effect on diagnostic ratings were explored, such as gender, year of graduation, and theoretical orientation of the respondents. Results of the statistical analyses failed to confirm evidence of heterosexual bias. Implications for further research and training are discussed.