1. A review of the literature has revealed that only two cases of an acute septic arthritis caused by Clostridium welchii have been reported. Both of these infections involved the knee.
2. Two new cases of an acute septic arthritis of the knee due to Clostridium welchii are discussed.
3. The varied clinical manifestations of Clostridium welchii as reported in the literature are briefly discussed.
4. It was observed that, in an acute septic arthritis due to Clostridium welchii, the local and systemic findings were of the nature and magnitude expected with any pyarthrosis due to more common organisms. Also, there was apparently little or no cartilage destruction with subsequent excellent functional recovery.
5. The primary purpose of this paper has been to establish Clostridium welchii as a possible cause of an acute septic arthritis.