This paper is based on baseline data from a survey of 1042 fifty-five year olds living in the Central Clydeside Conurbation, who constitute the eldest cohort of the 'West of Scotland Twenty-07 Study'--a longitudinal study of health and everyday life. The relationship between marital status and a number of measures of health and illness is explored. The paper examines which of four 'social causation' explanations--that married people have better health because they have more material resources, less stress, indulge in less risky health behaviour and have more social support--can actually account for the observed patterning. It finds that more risky health behaviour (measured by smoking and drinking), and 'objective' levels of social support, cannot account for very much of the effect of marital status on health measures; but that material resources, stress and perceived quality of social support could do so. However, elucidation of the direction of the relationships between these explanations and health measures, and indeed of the effect of health 'selection' into and out of marriage must await future sweeps of this longitudinal study.