Little research or attention has been focused on identifying sexual problems or difficulties that people with mental retardation commonly experience. Scale development represents an important area for study to help identify these problems and to evaluate treatment outcome. To address this need, the Psychopathology Instrument for Mentally Retarded Adults-Sexuality Scale (PIMRA-S) was designed to assess psychosexual disorders in mild and moderate mentally retarded persons. Eighty-six mild and moderately mentally retarded adults, ages 20 to 60, were studied using the PIMRA-S. Scale development of this type was considered important because little has been done to assess sexual problems among mentally retarded persons. Fifty-eight items were developed based on evaluations of the research literature and interviews of experienced professionals. A preliminary assessment of reliability was conducted. The psychometric characteristics of these preliminary analyses were favorable. In addition, information was reported on the rate of sexually aberrant behavior exhibited by people identified with mild and moderate mental retardation. Differences in the rate of sexually aberrant behavior were addressed as a function of living and work placement, positive history of sexual abuse, need for treatment of sexual problems, and psychiatric diagnosis. Implications of these results for further scale development are discussed.