Knowledge regarding substance-related problems and offending behavior in individuals with mild intellectual disability or borderline intellectual functioning (MBID; IQ 50-85) has increased over the last years, but is still limited. The present study examined differences in prevalence and clinical characteristics of individuals with and without MBID in a forensic addiction treatment center. Participants were 190 court mandated male clients of a low to high security forensic addiction treatment center in the Netherlands (aged between 21 and 59 years old, 82% of Dutch origin). Of the total sample 39% could be identified with MBID which is much higher than the estimated 12% to 15% of the general population. Results showed that clients with MBID reported significantly lower scores on desire for help, compared to clients without MBID (F (1, 73) = 5.12, p = .027). Against expectations, no significant group differences were found for aggression during treatment while controlling for impulsivity, treatment duration and type of substance use and offense. As results of the present study showed that clients with MBID are overrepresented in the forensic addiction treatment center, future research should further explore characteristics and responses to treatment of these clients. More knowledge about the characteristics of clients with MBID will not only help to better identify these clients, but will also to improve treatment for this group.