AbstractBackground Prospective studies in the general population are needed to identify risk factors for mental disorders. Samples of sufficient size are needed, but large-scale studies that assess the incidence of psychopathology are rare. Aims The aim of this study was to investigate the 12-month first incidence rates (IR) by age and gender for 15 specified DSM-III-R disorders in the general population. Methods The study was based on a representative sample (N = 5618) of the Dutch population aged 1864. Results The IR for any disorder was 5.68 per 100 person-years at risk (men 4.45, women 6.94). IRs for both men and women were highest in the youngest age category. The most common 12-month incident disorders in men were alcohol abuse (IR = 4.09) and major depression (1.72). In women, the most common incident disorders were major depression (IR = 3.90) and simple phobia (3.17). Conclusions The results show the rarity of first-onset of mental disorders. IRs vary strongly between the different life phases, as well as between men and women. This suggests potential target areas for age-specific and gender-specific prevention.