Patients with Evans syndrome have both immune thrombocytopenia and autoimmune hemolytic anemia, but little is known about the epidemiology of this rare syndrome. Evans syndrome can be primary or secondary. This nationwide retrospective study linked health registries to identify 242 patients with Evans syndrome in Denmark in 1977-2017. For comparison, we identified three age-matched and sex-matched cohorts of patients with only immune thrombocytopenia or only autoimmune hemolytic anemia, and a general population cohort. The Evans syndrome cohort had a mean age of 58.5 years at diagnosis, 51.2% were women, and 27.3% were classified as secondary Evans syndrome. The annual Evans syndrome incidence and prevalence rose significantly during the study period, to 1.8 per million person-years and 21.3 per million persons, respectively, in 2016. The median survival with Evans syndrome was 7.2 years (primary Evans syndrome: 10.9 years; secondary Evans syndrome: 1.7 years). Secondary Evans syndrome was associated with higher mortality rates than any of the other cohorts, with a 5-year survival of 38%. Among patients with Evans syndrome, the prevailing causes of death were bleeding, infections, and hematological cancer. In conclusion, we found that both primary and secondary Evans syndrome conferred a poor prognosis. Lethal complications probably derive primarily from manifestations of underlying autoimmune hemolytic anemia and immune thrombocytopenia. Our findings suggested that suspicion of Evans syndrome should prompt vigilant clinical follow-up. International collaborations are warranted to advance our knowledge of optimal management of this rare disease.