A case of a 6-year-old male child was studied. Initially, he presented large-joint arthritis of the right knee and heel, with clinical data of systemic inflammation, such as fever, increase in sedimentation rate and leucocytosis, during more than six weeks of evolution. A wrong initial diagnosis of septic arthritis was made, but the lack of response to antibiotics and surgical drainage of the knee led to a trial with prednisone, which induced clinical remission. The patient remained hospitalized for 24 days and underwent surgical drainage, knee arthroscopy, two bone gammagrams, nuclear magnetic resonance, and antibiotics, as well as considerable stress and uncertainty for him and his family. Thus, it is very important to make an early diagnosis of juvenile rheumatoid arthritis and avoid complications. Recent literature was examined with special emphasis on opportune clinical diagnosis, as well as on therapeutic innovations, which have been able to modify the course of the disease and improve the quality of life of these patients. Pediatricians and general practitioners should take into account this diagnosis when seeing a patient with arthritis, especially when the signs point towards a systemic disease affecting two or more joints.