OBJECTIVE: Positive psychological well-being is associated with reduced risk of chronic illnesses. Biological risk factors may contribute to these effects, although sex differences may be present. Two aspects of well-being can be distinguished: affective well-being (happiness and pleasure) and eudaemonia (sense of autonomy and purposeful engagement with life). We evaluated relationships between both affective and eudaemonic well-being and biological measures in a large sample of older people. METHODS: This cross-sectional study analyzed the English Longitudinal Study of Ageing, a nationally representative cohort aged 50 years or older. In this study, 7795 participants completed positive well-being and depressive symptom measures. Waist circumference, dehydroepiandosterone sulfate, C-reactive protein, fibrinogen, high-density lipoprotein cholesterol, plasma triglycerides, and peak expiratory flow were assessed. RESULTS: In men, affective well-being was associated with smaller waist circumference (B = -0.206, p .001) and greater levels of dehydroepiandosterone sulfate (B = 0.072, p = .003). Affective well-being in women was related to lower concentrations of inflammatory markers (C-reactive protein and fibrinogen, B = -0.242 and -0.024, respectively, p .001) and greater high-density lipoprotein cholesterol (B = 0.011, p = .017). Both men and women showed associations between well-being and lower levels of plasma triglycerides (B = -0.032, p .001) and better lung function (B = 3.594, p .001). Associations were independent of age, marital status, socioeconomic circumstances, body mass, smoking, limiting long-standing illnesses, health indicators, and depressive symptoms. Similar results were obtained for eudaemonic well-being. CONCLUSIONS: Positive psychological well-being has biological correlates that may be health protective, with distinctive patterns for men and women.