A sample of 436 persons of both sexes, all ages and being from all over the Lebanese territory, was analysed as part of a survey on the prevention of cardiovascular diseases. Our results gave an estimation of the prevalence of diabetes mellitus in Lebanon being at 7-8% and that of impaired glucose tolerance being at 10-11%. 50% of diabetics were previously unknown; this percentage rose up to 89% in people aged less than 40 years. The male preponderance was not statistically significant. The prevalence of diabetes mellitus increased steadily with age.