['To determine whether rubella virus (RV) is involved in the pathogenesis of Fuchs heterochromic iridocyclitis (FHI).', 'Retrospective patient-controlled study.', 'Intraocular immunoglobulin G production against RV, herpes simplex virus (HSV), varicella zoster virus (VZV), and Toxoplasma gondii was determined in the aqueous humor of 14 patients with FHI, 13 control subjects with herpetic uveitis anterior, and 19 control subjects with ocular toxoplasmosis by calculation of the Goldmann-Witmer coefficient (GWC).', 'All patients and control subjects were seropositive for RV. Intraocular antibody production (GWC >3) against RV was found in 13 of 14 patients (93%) with FHI. Intraocular antibody production against HSV, VZV, or T gondii was not detected. None of the control subjects with herpetic uveitis anterior or with toxoplasma chorioretinitis had a positive GWC for rubella virus (P < .0001, Fisher exact test).'] Is rubella virus associated with fuchs heterochromic iridocyclitis?