We studied characteristics of ocular inflammation associated with Yersinia infection in 23 patients. After an acute onset with fever, diarrhea, and abdominal pain, 22 patients developed arthritis, 11 patients developed myalgia, 11 patients developed Reiter's syndrome, 17 patients developed acute anterior uveitis, and nine patients developed conjunctivitis. Sacroiliitis was found in 12 patients. The patients had high erythrocyte sedimentation rates, leukocytosis, and lack of antinuclear antibodies and rheumatoid factor. All 17 patients tested had HLA-B27 antigen. The patients with acute anterior uveitis showed aqueous flare, cells, fine keratic precipitates, and often exudates, posterior synechiae, vitritis, and macular edema. Acute anterior uveitis was mostly unilateral and resolved during corticosteroids on the average during the first six weeks; recurrences were seen in about half of the cases. Conjunctivitis was generally mild with no chemosis, follicles, or keratitis; and it resolved in one week without treatment. Our results indicate that in HLA-B27 positive patients infective agents can trigger acute anterior uveitis or conjunctivitis, which often occur together with rheumatic diseases.