This randomised controlled experiment tested whether a brief subjective well-being intervention would have favourable effects on cardiovascular and neuroendocrine function and on sleep. We compared 2 weeks of a gratitude intervention with an active control (everyday events reporting) and no treatment conditions in 119 young women. The treatment elicited increases in hedonic well-being, optimism and sleep quality along with decreases in diastolic blood pressure. Improvements in subjective well-being were correlated with increased sleep quality and reductions in blood pressure, but there were no relationships with cortisol. This brief intervention suggests that subjective well-being may contribute towards lower morbidity and mortality through healthier biological function and restorative health behaviours.