Four cases of infectious arthritis due to beta hemolytic streptococci, Lancefield Group G are described. Three patients presented with acute polyarthritis involving unusual sites while the 4th patient had acute monoarthritis. All 4 cases had underlying diseases which predisposed them to infection: alcoholism (2 cases), malignant disease (1 case) and diabetes mellitus (1 case). Three patients had coexistent Group G streptococcal infection: endocarditis in 2 and skin infection in 1. With adequate parenteral antibiotic therapy and frequent joint aspiration, the prognosis for return of normal joint function following infection with Group G streptococcus appears to be excellent. These cases demonstrate the need for routine serogrouping of streptococcal isolates in patients with septic arthritis. The importance of recognizing this uncommon type of infectious arthritis is emphasized in view of its prognostic and therapeutic implications.