In a retrospective study (1963--1976) out of 514 children with the general diagnosis of arthritis, the diagnoses most frequently established were; pyogenic arthritis (45.9%), rheumatic fever (18.7%) and juvenile rheumatoid arthritis (17%). Less frequent were tuberculous arthritis (5.8%), systemic lupus erythematosus (3.9%), hemophilic hemarthrosis (2.1%), and other connective tissue diseases (1.5%). Age of onset was significantly lower in patients with pyogenic arthritis. Pyogenic, tuberculous and hemophilic arthritis in most cases were characterized by large joint monoarthritis. Acute polyarthritis was common in rheumatic fever. Chronic polyarthritis was a frequent feature in the other cases. It is concluded that age of onset, number and site of affected joints, as well as evolution time may be useful in the diagnosis.