The clinical features of idiopathic uveitis were compared by the seropositivity for human T-cell lymphotropic virus type I. The statistical analysis of various clinical variables disclosed that the uveitis seen in seropositive patients (93 patients) had a significantly higher incidence of floaters, vitreous opacities, retinal vasculitis, and intermediate uveitis than that in seronegative patients (222 patients) (P < .05). The odds ratios of the virus infection for these clinical manifestations were high and statistically significant, suggesting that the virus infection has a role as a risk factor for the development of these clinical manifestations. Although visual acuity at the initial examination was almost equal between the two groups, after the therapy with topical or systemic corticosteroids, or both, visual acuity in seropositive patients was much better than that in seronegative patients. The surface phenotype of peripheral lymphocytes in the two groups was compared as follows: CD4-positive T lymphocytes (P < .05), CD4/8 ratio (P < .01), and CD25-positive T lymphocytes (P < .05) were significantly higher in seropositive patients than in seronegative patients.