Objective: The aim of this study was to investigate associations between underweight, overweight and obesity in young adult men and risk of disability pension (DP) due to psychiatric disorders. Design and subjects: In this nationwide study of 1 110 139 Swedish men (mean age 18.3 ± 0.5 years), weight, height and muscular strength were measured at mandatory military conscription testing . Information on DP , residential area, parental socioeconomic position and education and preexisting psychiatric disorders was obtained by record linkage of national registers. Results: During 26 million person-years of follow-up, 19 684 men received DP due to psychiatric disorders. After adjustment, hazard ratios (HRs) due to any psychiatric disorder were 1.20 (95% CI: 1.15-1.26) for underweight, 1.14 (95% CI: 1.08-1.21) for overweight and 1.43 (95% CI: 1.28-1.60) for obesity compared to normal weight. For affective disorders, HRs were elevated for underweight (1.24, 95% CI: 1.16-1.32), overweight (1.19, 95% CI: 1.10-1.28) and obesity (1.55, 95% CI: 1.33-1.81), whereas for substance abuse increased risks were seen only for underweight (1.41, 95% CI: 1.23-1.61) and obesity (1.50, 95% CI: 1.07-2.12). For nonaffective disorders (including schizophrenia) overweight (HR ¼ 0.87, 95% CI: 0.76-1.00) and obesity (HR ¼ 0.79, 95% CI: 0.57-1.10) seemed to be protective, although not statistically significant. HRs for personality disorders were increased for underweight (1.18, 95% CI: 1.04-1.34), overweight (1.16, 95% CI: 1.00-1.30) and obesity (1.40, 95% CI: 1.03-1.90). Conclusion: Underweight and overweight were associated with small risk increases, whereas higher risks for DP were generally found for obesity.