Background: Tuberous sclerosis (TS) is a multi- system disorder with complex genetics. The neurodevelopmental manifestations of TS are responsible for considerable morbidity. The prevalence of epilepsy and intellectual disabilities among individuals with TS have been well described. Ours is the first study that explores the prevalence and pattern of psychopathology in a population-based sample of adults with TS. Methods: Sixty subjects were identified through a capture--recapture analysis of TS. Information was gathered as to seizure history, cognitive functioning (WISC-III) and psychopathology (SADS-L, SAPPA). Lifetime psychopathology was categorized according to Research Diagnostic Criteria. The overall pattern of mental illness (MI) was examined as well as how this varied with IQ and seizure history. Results: Twenty-four (40.0%) subjects had a history of MI. The most common diagnosis was that of an affective disorder [18 (30.0%)], the majority of which were major depressive episodes. Alcoholism [4 (6.7%)] and anxiety disorders [3 (5.0%)] were the next most common diagnoses. Two (3.3%) subjects had had a tic disorder. Only one individual had a diagnosis of schizophrenia. MI was found in 75.0% of those with a history of epilepsy and 37.5% of those without epilepsy. MI was significantly more prevalent in those with a full-scale IQ above 70. Conclusions: A significant proportion of adult with TS experience MI. MI was significantly less prevalent in subjects with a full-scale IQ above 70. Reasons for such a finding are explored, and related methodological considerations for future research outlined.