Four decades of suicide mortality data for England and Wales were analysed within an age-period-cohort framework. Marked differences in results were found by sex. The analysis of the male data showed that the risk of suicide increased with age until men were in their mid-fifties (after allowing for period and cohort effects), and that suicide risk declined for males born from 1876 to 1915, but had increased over 4-fold for certain later-born cohorts. Female suicide risk was found to decline with later nativity (after adjusting for age and period effects). The identification of period effects in terms of known changes in the carbon monoxide (CO) content of domestic gas successfully accounted for temporal variation in male suicide risk, but fitted less well to the data for females.