OBJECTIVE: The aim of this study was to describe the clinical manifestations and to assess the occurrence of atypical arthritis in ARF patients attending a Pediatric Rheumatology Clinic at the University Hospital of Ribeirão Preto. METHODS: We have studied retrospectively the records of 120 attacks of ARF in 109 children, 3-13 years old, who attended our clinic from January 1990 to December 1995. All children fulfilled the Jones criteria. RESULTS: 77% of the attacks involved arthritis, 62% carditis, 32% chorea, 2.5% subcutaneous nodules and 1.3% erythema marginatum. The number of involved joints was 1 in 3 episodes of ARF, 2-5 in 52, 6-10 in 30 and more than 10 in 5. Arthritis was considered atypical in 43 (47%) of the 92 ARF episodes with arthritis, based on the following criteria: involvement of unusual joints (cervical spine in 24 children, hip in 15, small joints of the hand in 12 or feet in 13); monarthritis (3); duration longer than 3 weeks (26); incomplete response to salicylates (18). Association of these atypical features were frequently present. For instance, considering the 24 episodes with cervical spine involvement, the duration of arthritis was longer than 3 weeks in 13 cases, 10 had insufficient response to salicylates and the hip joint was also involved in 7. Time to reach diagnosis was longer than 4 weeks in 59% of the patients presenting with atypical arthritis compared to 35% in the other patients (p=0.04). Different diagnosis were considered at the beginning of the disease in 40% of the 120 episodes and in 65% of the ones presenting with atypical arthritis (p=0.03). CONCLUSION: We conclude that atypical arthritis was present in a significant proportion of ARF episodes, adding an extra dilemma to the diagnosis of this intriguing disease.