Chronic recurrent multifocal osteomyelitis (CRMO) is an unusual form of non-microbial chronic osteomyelitis. It is an exclusion diagnosis that can only be considered after ruling out infectious osteomyelitis and bone tumors. We report the case of a 13-year-old girl who was admitted for a painful swelling of the left thigh. Biological examinations did not find an inflammatory syndrome. X-rays and Magnetic Resonance Imaging were very suggestive of malignant bone tumor. But the biopsy disclosed a nonspecific osteomyelitis. Considering the strong suspicion of a malignant origin, a second biopsy was performed and confirmed the diagnosis of osteomyelitis. During the hospital stay, the patient developed a second location in the left humerus. Thus, the diagnosis of CRMO was retained. The patient was treated by NSAIDs with good clinical and radiological outcomes. This case report reminds the diagnostic challenge of this pathology that can mimic malignant tumor.