In a population of 564 patients with rheumatoid arthritis (RA), the onset of symptoms has been studied in relation to age, sex and last menstrual period for women. Median age of menopause was 49 years (3rd percentile: 32 years and 97th percentile: 56 years). Median age of first symptoms was 45 years in women and 50 in men. The individual interval between menopause and first symptoms has a Gaussian distribution with mean at time 0, implying that the average woman develops the first symptoms at the time of her menopause. The F:M ratio of all patients was 2.3; with increasing age the F:M ratio decreased from 3.7 before 30 years of age to 1 after the 6th decade of life, with a peak at the age of 40-44 years. A possible effect of age related changes in sex hormone levels on the pathogenesis of RA is suggested.