Emerging research is beginning to uncover a high prevalence of modifiable risk factors in patients with severe mental illness. We examined whether the association between episodes of psychiatric illness that involved hospitalization and all-cause mortality is mediated by behavioral risk factors. Data were collected from a nationally representative sample of 19 898 men and women from the Scottish Health Surveys (1995, 1998, and 2003) that were linked to a patient-based database of hospital admissions and deaths up to September 2006. There were 597 participants with at least 1 hospital admission for a psychiatric episode. During a mean follow-up of 8.5 years, participants with a history of a psychiatric episode had a higher risk of all-cause mortality (age- and sex-adjusted hazard ratio, 3.25; 95% confidence interval, 2.63-4.02). In addition, they were more likely to be heavy smokers (odds ratio, 4.69; 95% confidence interval, 3.79-5.82), have low physical activity levels (2.24; 1.75-2.87), come from a lower socioeconomic group (2.17; 1.72-2.72), and be separated or divorced from their partner (2.02; 1.63-2.52). In multivariate analyses, the association between history of a psychiatric episode and all-cause mortality was attenuated but remained statistically significant (hazard ratio, 2.02; 95% confidence interval, 1.62-2.52; P<.001) after adjustments for psychosocial factors, smoking, physical activity, body mass index, and current mental health. Behavioral risk factors may partly mediate the association between psychiatric episodes and mortality. These data highlight the need for prevention and treatment strategies among individuals with a history of severe mental illness.