Sexual Orientation–Obsessive-Compulsive Disorder (SO-OCD) is characterized by intrusive thoughts, images, and urges related to one’s sexual orientation, and by consequent avoidance, reassurance seeking, and overt and covert compulsions. Currently there is no short self-report measure that assesses SO-OCD symptoms. The current article describes two studies that develop and evaluate the first version of the Sexual Orientation Obsessive-Compulsive Scale (SO-OCS), a 14-item Italian self-report measure targeted towards heterosexual individuals. In Study 1, the SO-OCS was developed and refined through item analysis and exploratory factor analysis from an initial pool of 33 items administered to 732 Italian nonclinical participants. The SO-OCS showed a unidimensional structure and an acceptable internal consistency. In Study 2, the factor structure, internal consistency, temporal stability, construct and criterion validity, and diagnostic sensitivity of the SO-OCS were investigated in three samples of Italian participants (294 from the general population, 52 OCD patients who reported sexual orientation-related symptoms or concerns as a primary complaint, and 51 OCD patients who did not report these symptoms as primary complaint). The SO-OCS was again found to have a unidimensional structure and good internal consistency, as well as to exhibit strong construct validity. Specifically, the SO-OCS showed an excellent criterion validity and diagnostic sensitivity, as it successfully discriminated between those with SO-OCD and all other groups of participants. Finally, evidence of temporal stability of the SO-OCS in a nonclinical subsample was found. The SO-OCS holds promise as a measure of SO-OCD symptoms in heterosexual individuals.