The relationship between unemployment and mental well-being was studied in 703 Finnish women and men who were originally employed in industry (manufacturing). A population survey with a follow-up measurement was carried out in 1983 and 1984. Mental well-being was measured by a 12-item version of the General Health Questionnaire. The association between unemployment and mental ill-health proved to be a strong one. Cross-sectional analyses and analyses on the improvement of mental well-being were made. The impact of employment status on mental ill-health, as well as its improvement, was controlled for by means of logistic regression analysis (GLIM). Several variables included in the design did not alter the main result, apart from the fact that the impact of unemployment was stronger among men than among women. The impact of unemployment proved to be independent and direct. The author compares these results with other studies that have used a similar approach, and discusses the significance of paid work in developed capitalist societies in an understanding of the adverse impacts of unemployment.