Risk reduction in patients with clinically manifest vascular disease focuses on preventing new vascular events and not on prevention of type 2 diabetes. However, given the common pathophysiological pathways involved in the development of atherosclerosis and type 2 diabetes, it is probable that people with atherosclerotic vascular disease have an elevated risk of type 2 diabetes. The present prospective cohort study investigated the incidence of type 2 diabetes and the effect of the presence of metabolic syndrome on the incidence of type 2 diabetes in 4,022 patients with clinically manifest atherosclerosis, included in the study from September 1996 to June 2006. Patients who died (n=456), who were lost to follow-up (n=84) and those with diabetes at baseline (n=558) were excluded, leaving 2,924 patients for analysis. The incidence of diabetes was assessed by questionnaire (self-reported diabetes). During 13,726 person-years of follow-up (median follow-up 4.3 years, range 2.4-7.0 years), there were 152 type 2 diabetes cases (5.2%), corresponding to an incidence rate of 11.1 (95% CI 9.4-13.0) per 1,000 person-years. Patients with metabolic syndrome were at increased risk of incident type 2 diabetes compared to those without metabolic syndrome, with an adjusted hazard ratio of 5.7 (95% CI 3.7-8.9) for Revised National Cholesterol Education Program, 6.0 (4.1-9.0) for National Cholesterol Education Program and 4.0 (2.7-6.1) for International Diabetes Federation definitions of metabolic syndrome. Of all metabolic syndrome components, abdominal obesity was most strongly associated with incident type 2 diabetes (94% higher risk of type 2 diabetes for 1 standard deviation (11.3 cm) increase in waist circumference). In conclusion, patients with manifest atherosclerosis are at high risk of developing type 2 diabetes. Metabolic syndrome identifies those at the highest risk and is an easy to use clinical tool. Abdominal obesity is a strong individual predictor of type 2 diabetes. Patients with manifest atherosclerosis and metabolic syndrome may derive particular benefit from lifestyle interventions focusing on weight reduction.