Objectives: To determine the characteristics of adult-onset autoimmune chorea, and compare paraneoplastic and idiopathic subgroups. Methods: Thirty-six adults with autoimmune chorea were identified at Mayo Clinic (Rochester, MN) from 1997 to 2012. Medical record and laboratory data were recorded. Nonparaneoplastic (n = 22) and paraneoplastic cases (n = 14) were compared. Results: Women accounted for 21 patients (58%). Median age at symptom onset was 67 years (range 18-87 years). We estimated the incidence for Olmsted County was 1.5 per million person-years. Symptom onset was subacute in all. Chorea was focal (20 patients) or generalized (16 patients). Although chorea predominated, other neurologic disorders frequently coexisted (29 patients); abnormal eye movements were uncommon (4 patients). No patient had NMDA receptor antibody or any immunoglobulin (Ig)G yielding a detectable immunofluorescence binding pattern restricted to basal ganglia. Two had synaptic IgG antibodies novel to the context of chorea (GAD65,1; CASPR2,1). In the paraneoplastic group, 14 patients had evidence of cancer. Of 13 with a histopathologically confirmed neoplasm, small-cell carcinoma and adenocarcinoma were most common; 6 patients had a cancer-predictive paraneoplastic autoantibody, with CRMP-5-IgG and ANNA-1 being most common. In the idiopathic group, 19 of the 22 patients had a coexisting autoimmune disorder (most frequently systemic lupus erythematosus and antiphospholipid syndrome); autoantibodies were detected in 21 patients, most frequently lupus and phospholipid specificities (19 patients). The paraneoplastic group was older (p = 0.001), more frequently male (p = 0.006), had more frequent weight loss (p = 0.02), and frequently had peripheral neuropathy (p = 0.008). Conclusions: Autoimmune chorea is a rare disorder with rapid onset. Male sex, older age, severe chorea, coexisting peripheral neuropathy, and weight loss increase the likelihood of cancer.