OBJECTIVE In the Netherlands, patients with borderline intellectual functioning are eligible for specialized mental health care. This offers the unique possibility to examine the mix of psychiatric disorders in patients who, in other countries, are treated in regular outpatient mental health care clinics. Our study sought to examine the rates of all main Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, Text Revision, Axis I psychiatric diagnoses in outpatients with borderline intellectual functioning of 2 specialized regional psychiatric outpatient departments and to compare these with rates of the same disorders in outpatients from regular mental health care (RMHC) and outpatients with mild intellectual disabilities (IDs). METHOD Our study was a cross-sectional, anonymized medical chart review. All participants were patients from the Dutch regional mental health care provider Rivierduinen. Diagnoses of patients with borderline intellectual functioning (borderline intellectual functioning group; n = 235) were compared with diagnoses of patients from RMHC (RMHC group; n = 1026) and patients with mild ID (mild ID group; n = 152). RESULTS Compared with the RMHC group, psychotic and major depressive disorders were less common in the borderline intellectual functioning group, while posttraumatic stress disorder and V codes were more common. Compared with the mild ID group, psychotic disorders were significantly less common. CONCLUSION Mental health problems in people with borderline intellectual functioning may not be well addressed in general psychiatry, or by standard psychiatry for patients with ID. Specific attention to this group in clinical practice and research may be warranted lest they fall between 2 stools.