We describe 2 cases of arthritis following immunization against diphtheria, poliomyelitis and tetanus toxoid. One patient developed monoarthritis of the knee after immunization, that regressed following synovectomy. Five years later, the arthritis recurred after a booster vaccine injection. One day after immunization, another patient developed arthritis of the ankle that persisted for 3 days. It is difficult to know whether there is a coincidental or a causal relation between immunization and arthritis. Although our cases suggest that immunization against diphtheria, poliomyelitis and tetanus toxoid may cause arthritis, additional cases must be reported before studies aimed at confirming this possibility are considered.