OBJECTIVES: The prevalence of metabolic syndrome (MS) in HIV-infected patients on highly active antiretroviral therapy (HAART) is a subject of debate. We investigated the prevalence of MS in a cohort of Danish HIV-infected patients and estimated the effect of the various classes of antiretroviral therapies on the prevalence of MS and its components. METHODS: A cross-sectional study was performed in which data were obtained from fasting blood tests, anthropometry, an interview questionnaire and whole-body dual-energy X-ray absorptiometry (DEXA) scans. MS was defined using the National Cholesterol Education Programme (NCEP) Adult Treatment Panel (ATP) III diagnostic criteria. RESULTS: Five hundred and sixty-six patients were included in the study, of whom 27% were diagnosed with MS. In univariate analysis, the duration of treatment with different drug classes was associated with the prevalence of MS. In multivariate analysis, no association was demonstrated between therapeutic duration or modality and the occurrence of MS. Current nonthymidine reverse transcriptase inhibitor (NRTI) and protease inhibitor (PI) therapies were both associated with increased plasma triglycerides (TG) [odds ratio (OR) 3.42, 95% confidence interval (CI) 1.73-6.74; and OR 1.96, 95% CI 1.19-3.22, respectively]. CONCLUSIONS: MS is prevalent in HIV-infected Danes. However, treatment with specific drug classes does not seem to confer an elevated risk for MS, other than the risk conferred by known acute effects on triglycerides.