Background. Insomnia and disability pension are major health problems, but few population-based studies have examined the association between insomnia and risk of disability pension. Methods. We conducted a prospective nationwide cohort study based on Swedish population-based registers including all 5,028,922 individuals living in Sweden on December 31, 2004/2005, aged 17–64 years, and not on disability or old age pension. Those having at least one admission/specialist visit with a diagnosis of disorders of initiating and maintaining sleep (insomnias) (ICD-10: G47.0) during 2000/2001–2005 were compared to those with no such inpatient/outpatient care. All-cause and diagnosis-specific incident disability pension were followed from 2006 to 2010. Incidence rate ratios (IRRs) and 95% confidence intervals (CIs) were estimated by Cox regression. Results. In models adjusted for prior sickness absence, sociodemographic factors, and inpatient/specialized outpatient care, associations between insomnia and increased risks of all-cause disability pension (IRR 1.35, 95% CI 1.09–1.67) and disability pension due to mental diagnoses (IRR 1.86, 95% CI 1.38–2.50) were observed. After further adjustment for insomnia medications these associations disappeared. No associations between insomnia and risk of disability pension due to cancer, circulatory, or musculoskeletal diagnoses were observed. Conclusion. Insomnia seems to be positively associated with all-cause disability pension and disability pension due to mental diagnoses.