We evaluated the safety and efficacy of tocilizumab in polyarticular-course juvenile idiopathic arthritis (pJIA) with polyarticular or oligoarticular onset. Patients received 8 mg/kg tocilizumab every 4 weeks in the open-label studies: initial study (to week 12) and then an extension study (at least 48 weeks). Nineteen patients intractable to conventional methotrexate therapy were enrolled. Seventeen patients had polyarticular-onset pJIA; two had oligoarticular-onset pJIA. Mean age was 11.6 years; mean disease duration 5.3 years. American College of Rheumatology Pediatric (ACR Pedi) 30, 50, 70, and 90 response rates, respectively, were 94.7%, 94.7%, 57.9%, and 10.5% at week 12, and 100%, 94.1%, 88.2%, and 64.7% at week 48. Mean disease activity score (DAS28) remained below the remission level (2.6) from week 24. Administration was discontinued in two patients during the extension study because the ACR Pedi 50 response was judged insufficient (one patient) and antitocilizumab antibodies developed (one patient). Adverse events were generally mild, and the four serious adverse events resolved spontaneously or with treatment. In conclusion, tocilizumab showed early and sustained efficacy and tolerability for treating intractable pJIA, which suggests that it is a promising new treatment for this disease.