Background: Adult survivors of childhood cancer have been reported to have an increased risk of late sequels. A cluster of abnormalities that contribute to the metabolic syndrome may be expressed at a higher level and therefore result in an increased risk for diabetes mellitus and cardiovascular diseases. Patients and methods: We investigated a single-centre cohort of 500 adult survivors (228 females) of childhood cancer, median age 28 years (range 18-59 years) and median follow-up time 19 years (range 6-49 years). We measured total cholesterol, high-density lipoprotein-cholesterol, systolic and diastolic blood pressure, body mass index and the prevalence of diabetes mellitus. Data from the epidemiological Monitoring van Risicofactoren en Gezondheid in Nederland (MORGEN) study were used to calculate standard deviation scores as normative values. Results: The criteria of the metabolic syndrome were met in 13% of the total cohort. Acute lymphoblastic leukaemia (ALL) survivors treated with cranial irradiation had an increased risk of developing the metabolic syndrome compared with ALL survivors not treated with cranial irradiation (23% versus 7%, P = 0.011), probably determined by higher prevalence of overweight and hypertension. Conclusion: Adult survivors of childhood cancer, especially those treated with cranial irradiation, are at increased risk of developing the metabolic syndrome.