This paper presents a case report of a 15-year-old boy admitted to the hospital for persistent right knee pain and limping. The clinical appearance of his condition was the basis on which diagnosis of chronic recurrent multifocal osteomyelitis was made. Continuous deterioration in the clinical status also led to a suspicion of the presence of other pathological processes. A bone biopsy was performed and the results of histopathology showed diffused large cell B lymphoma. Chemotherapy was initiated; nevertheless, the patient’s general state worsened gradually and subsequent pancytopenia resulted in septicemia and multiorgan failure that led to the patient’s death. This paper reports the exceptional diagnostic challenges that emerged from the obscure course of the disease.