Two siblings infected with Yersinia pseudotuberculosis suffered from acute renal failure about 2 weeks after the onset of the disease. Renal histology in both siblings showed acute tubulointerstitial nephritis. Yersinia pseudotuberculosis type VB was isolated from feces of one of them, antibodies to Yersinia pseudotuberculosis type VB in their sera were elevated. The results of the present study suggest that acute renal failure complicating infections with Yersinia pseudotuberculosis is due to acute tubulointerstitial nephritis.