Objective: To examine whether serum levels of a-tocopherol, b-carotene and retinol were associated with risk of non-insulin dependent diabetes mellitus (NIDDM). Design and subjects: The study design was a nested case-control study within a longitudinal population study. Serum levels of antioxidants were determined in 106 incident cases with non-insulin dependent diabetes mellitus detected on follow-up and 201 controls matched for sex, age and study region. Results: The incident cases had lower serum a-tocopherol and b-carotene levels than controls. The relative risk between the highest and lowest tertiles of serum a-tocopherol was 0.61 (95% con®dence interval (CI) 0.32±1.15), between the highest and lowest tertiles of serum b-carotene 0.45 (CI 0.22±0.92). Although the relative risk of highest compared with lowest tertile of serum a-tocopherol was not statistically signi®cant the inverse trend through the tertiles was (P`0.05). The decreasing risk of diabetes was particularly evident in the elderly, women, nonsmokers and the obese. However, adjustment for serum cholesterol, obesity, smoking and hypertension abolished the associations. The adjusted relative risks in relation to serum a-tocopherol and bcarotene (between highest and lowest tertiles) were 1.25 (CI 0.54±2.90) and 0.94 (CI 0.38±2.32), respectively. No associations were observed relating to serum retinol. Conclusions: High levels of a-tocopherol and b-carotene were found to be associated with decreased risk of noninsulin dependent diabetes mellitus, but the association disappeared after adjustment for cardiovascular risk factors.