Undifferentiated arthritis comprises a heterogenous group of arthritides. Their common feature is the fact that arthritis cannot be classified according to contemporary diagnostic criteria into clearly defined rheumatological groups. The clinical picture is usually varied, in some instance very similiar to that of reactive arthritis. From the literature it is known that in patients with undiffe- rentiated arthritis relatively frequently latent urogenital or intestinal infections are detected. So far it is not clear whether there exists a causal relationship between latent infection and undiffe- rentiated arthritis. The author reviews information on this subject.

        Key words: undifferentiated arthritis, latent infection, reactive arthritis