The diagnosis personality disorder is often found among samples of adults with mild intellectual disability and severe behavioral and mental health disorders. The number of studies on the adverse effects of this diagnosis are scarce. Using vignets in the present study, we have explored the relationship between the diagnosis personality disorder and professionals' evaluation of treatment features. Professionals evaluate that in clients with this diagnosis treatment takes longer, a longstanding reduction in behavioral problems is less likely, focus of treatment is on adaptation of the context (instead of improving self-control) and that the setting after clinical treatment will be more restrictive than in clients without this diagnosis. There is a significant interaction effect between the diagnosis personality disorder and the variable motivation for treatment. Both of these variables strongly and mutually influence professionals' evaluation of treatment features.