A total of 288 mentally retarded offenders admitted to Florida State Hospital's Mentally Retarded Defendant Program (MRDP) were involved in this study. Offender characteristics were categorized into demographic, psychiatric or medical, and legal features. These data were obtained through a comprehensive review of MRDP offender files. Approximately 29 percent (n=82) of the sample were charged with a sex-related crime, and of this group 35 percent (n=29) had multiple charges that consisted of either sex-related or other felony crimes. To evaluate the effects of predictors in defining mental retardation, this study used an individual-level analysis across the mentally retarded offender's characteristics, which were handled as indicators of mental retardation. The study found that regardless of criminal charges, sex-related or not, offenders were more likely to be diagnosed as having severe mental retardation if they had a severe deficit in adaptive behavior or a low IQ score. Findings also show that mentally retarded sex offenders were rarely distinguishable from other retarded offenders in terms of mental retardation, IQ, and deficits in adaptive behavior. It is not valid, therefore, to assume that a simple definition of mental retardation, one based on IQ and adaptive behavior, is sufficient to determine either a viable diagnostic mechanism or an effective treatment program. 2 tables and 43 references