The aim of this study was to investigate the prevalence of diabetes mellitus, hypertension and cardiac complaints in a Dutch population with polycystic ovarian syndrome (PCOS) and to compare the results with the prevalence of these conditions in the Dutch female population, as retrieved from the Netherlands Health Interview Survey of Statistics Netherlands. A total of 346 PCOS patients were interviewed by telephone, with a mean age of 38.7 years (range 30.3--55.7) and a mean body mass index of 24.4 (range 17.5--55.8). Diabetes occurred in eight (2.3%), hypertension in 31 (9%) and cardiac complaints in three (0.9%) of the women. The prevalence of diabetes and hypertension differed significantly from the prevalence of these conditions in the Dutch female population (both P < 0.05). In PCOS women aged 45--54 years (n = 32) the prevalence of diabetes was four times higher (P < 0.05) and of hypertension 2.5 times higher (P < 0.01) than the prevalence of these conditions in the corresponding age group of the Dutch female population. Hypertension also occurred significantly (P < 0.05) more in the younger (35--44 years) PCOS group (n = 233), but this age group was significantly more obese (P < 0.01) when compared with figures of obesity of the Dutch female population. In conclusion, our data show that in a follow-up study of a relatively lean PCOS population, the prevalence of diabetes mellitus and hypertension was increased when compared with the Dutch female population, especially in women aged 45--54 years.