Sever's disease is juvenile osteochondrosis of calcaneus, manifested with posterior heel pain and mild swelling, usually in young athletes, caused by repetitive microtrauma. The standard diagnostic procedures include radiographs and ultrasound examination. It is a self-limiting condition, usually treated conservatively. We present a case of Sever's disease complicated with calcaneal osteomyelitis. A 9-year-old boy with a several month history of left heel pain was admitted to our institution for further clinical evaluation and therapy. Bilateral Sever's disease was clinically diagnosed, confirmed by radiographs and ultrasound examination. Magnetic resonance imaging (MRI) showed osteolytic zone in the posterior left calcaneus with peripheral enhancement after contrast administration and surrounding bone and subcutaneous edema, suggestive of osteomyelitis. After six weeks of parenteral antibiotic treatment, the patient's condition improved. Follow up MRI performed 3 months later showed significant regression of osteolytic lesion and replacement with granulation tissue surrounded with new bone formation. To our knowledge and literature search, this is a previously unreported complication of Sever's disease. MRI should be done in all atypical cases of Sever's disease to rule out any other possible disorders including osteomyelitis.