In 1971-73, 60 patients were hospitalized for an infectios disease caused by Y. enterocolitica serotypes III and IX or Y. pseudotuberculosis serotype I. In the spring of 1977 a follow-up study was carried out with 52 of these patients, one patient having died from intestinal perforation evidently resulting from yersiniosis-induced amyloidosis and colitis. The follow-up study showed that two patients had symptoms of sacroilitis, one had developed an apparent rheumatoid arthritis after yersiniosis and one had joint plans and a high serum rheumatoid factor titer with no objective joint changes. All results from kidney and liver studies were normal. No brucellosis antibodies were found in the follow-up study. Twelve patients had antibody titers against Y. enterocolitica serotype III.