Community studies found deficits of cognitive function in elderly persons with diabetes. The aim of the present study was to compare diabetes and other age-related diseases among residents of senior citizens' care facilities. Participants were 130 residents with and 130 without a diagnosis of diabetes aged between 65 and 98 years. Measures were neuropsychological tests designed for this age group, questionnaires of mood, quality of life and daily activities and level of glycosylated hemoglobin (HbA(1c)) as an index of metabolic control. Only verbal memory was significantly more impaired in residents with than without diabetes. Otherwise, both groups showed overall impairment of cognitive function and mood. Unexpectedly, a slightly elevated HbA(1c) level (6-8%) was associated with an increased level of cognitive and everyday functioning. In old age, diabetic patients might benefit from a slightly higher level of blood glucose than has hitherto been assumed.