BACKGROUND: Type 2 diabetes mellitus (T2DM) is associated with mild decrements in cognitive functioning, but the relation of these decrements to metabolic and vascular risk factors is unclear. The present study compared the vascular risk factor profile over the preceding 16 years between T2DM patients with good cognitive functioning and those with poor cognitive functioning. METHODS: The Hoorn study is a population-based cohort study on glucose metabolism and vascular disease initiated in 1989, with follow-up examinations in 1996-1998, 2000-2001 and 2005-2007. Cognitive functioning was assessed in 2005-2007. Patients who developed T2DM between 1989 and 2000-2001 (n = 64) were divided in tertiles (lowest tertile = 'poor cognition', highest tertile = 'good cognition') according to a sum score for performance across cognitive domains (SUM) and the domain score for information-processing speed (IPS). The time course of vascular risk factors from 1989 to 2005-2007 was compared between these tertiles with linear mixed models adjusted for age, sex and estimated IQ. RESULTS: Present levels (2005-2007) of vascular risk factors did not differ between patients with relatively poor or good cognition. However, patients with poor cognition had a 14-18 mmHg higher systolic blood pressure in 1989 than patients with good cognition. There were no differences in lipid profile and body weight at any time during the study between the groups. For IPS the T2DM patients with poor cognition even had a lower baseline HbA(1c) level than patients with good cognition. CONCLUSIONS: Cognitive dysfunction in T2DM is related to the cumulative effects of long-term exposure to hypertension, even in pre-DM stages. Copyright (c) 2009 John Wiley & Sons, Ltd.