Septic arthritis is rare in haemophiliacs. Four new cases who were also HIV positive are reported. In three, the knee was involved, and in the fourth the elbow. The organism was streptococcus pneumoniae and staphylococcus aureus in one patient each, and salmonella in two. Although all the patients were human immunodeficiency virus (HIV) positive at the time of diagnosis, only two patients developed autoimmune deficiency syndrome (AIDS) after their septic arthritis. These two died later due to AIDS complications. Treatment was conservative in all cases with antibiotic therapy and prompt rehabilitation. The results were fair in two and good in two. Therefore nonoperative management is advocated before surgical drainage is considered. It seems likely that a positive HIV status is related to the appearance of septic arthritis in haemophiliacs.