The causes of myeloproliferative neoplasm (MPN) are unknown. We conducted a large population-based study including 11,039 myeloproliferative neoplasm patients and 43,550 matched controls with the aim of assessing the associations between a personal history of a broad span of autoimmune diseases and subsequent risk of myeloproliferative neoplasm. We found a prior history of any autoimmune disease to be associated with a significantly increased risk of myeloproliferative neoplasms (odds ratio (OR)=1.2; 95% confidence interval (CI) 1.0-1.3; P=0.021). Specifically, we found an increased risk of MPNs associated with a prior immune thrombocytopenic purpura (2.9; 1.7-7.2), Crohn's disease (1.8; 1.1-3.0), polymyalgia rheumatica (1.7; 1.2-2.5), giant cell arteritis (5.9; 2.4-14.4), Reiter's syndrome (15.9; 1.8-142) and aplastic anemia (7.8; 3.7-16.7). The risk of myeloproliferative neoplasms associated with prior autoimmune diseases is modest but statistically significant. Future studies are needed to unravel the effects of these autoimmune diseases themselves, their treatment, or common genetic susceptibility.