The aim of our study was to identify the course of systemic onset juvenile idiopathic arthritis (SOJIA) based on the severity of both systemic and joint disease, incidence of remission (at 3, 5, 10 and 15 years post onset) and radiological changes (at 5, 10 and 15 years post onset) over the disease course. The study comprised 47 patients classified as having SOJIA with mean duration of disease of 18±7.4 years. Only 4.4% and 8.7% of our patients were in remission at 3 and 5 years after onset, while at 10 years – 18.6% and 15 years – 48.4%. Erosions occurred within 3,5 years of disease onset in 46% of cases. Severe radiological abnormalities were also common, occurring in 38% of patients within 5 years of disease and most commonly at 10 (64%) and 15 (72%) years after disease onset. 82.6% of patients had involvement of the hip; some of them required surgery. Only 27.9% of cases had systemic symptoms only within 6 months of disease onset. 72.1% of patients had persistent or relapsing systemic disease, some of them after prolonged remissions. The arthritis took several forms. Only 18.6% of our patients had joint disease grade of 1 or 2 (Bedford’s classification) while almost half of the patients (45.2%) had joint disease grade of 5 or 6 (number of joints involved 10 or more with functional incapacity or severe destructive joint disease with gross functional incapacity). In conclusion, the course of SOJIA is variable. Our study indicated that about half of patients with SOJIA develop severe polyarthritis with early radiological changes and remission occurs only in half of patients after 15 years of follow-up. The disease can reactivate even after many years of remission, sometimes during adulthood. On the other hand, some of the pa- tients have long-term complete remission with no disability or radiological changes after 15 years duration of the disease.