Type 2 diabetes mellitus (DM2) is a common metabolic disorder. DM2 is associated with cognitive impairments, and with depressive symptoms, which occur in about one third of patients. In the current study we compared the cognitive profile and psychological well-being of 119 patients with DM2 (mean age: 66 ± 6; mean duration: 9 ± 6 years) with 55 age and education matched-control participants. Groups were compared on cognitive performance in five major cognitive domains, psychological wellbeing [assessed by Symptom Checklist (SCL)-90-R and the Beck Depression Inventory (BDI-II)] and abnormalities on brain MRI. We hypothesized an interrelationship between cognition, MRI abnormalities, and psychological well-being. DM2 patients performed significantly worse than controls on cognitive tasks, especially on tasks that required more mental efficiency, although the differences were modest (effect sizes Cohen d < .6). We speculate that DM2 patients have a diminished ability to efficiently process unstructured information. Patients with DM2 had significantly higher scores on the SCL-90-R (p < .001) and on the BDI-II (p < .001) and worse MRI ratings than controls, but psychological distress did not correlate with cognition, MRI ratings or biomedical characteristics. Contrary to our hypothesis, cognitive disturbances and psychological distress thus seem independent symptoms of the same disease. (JINS, 2007, 13, 288–297.) [ABSTRACT FROM AUTHOR]