Eosinophilic granuloma (EG) is a rare histiocytic disorder resulting from clonal proliferation of Langerhans cells. It accounts for less than 1% of all osseous neoplasms and has a predilection for involving the axial skeleton. Although suspicion of the disease may arise from clinical features and radiographic demonstration of destructive bone lesions, it is still difficult to make a correct diagnosis without proper pathological evaluation. This is more evident when common differentials mimicking EG, both clinically and radiologically, need to be ruled out. This report describes a case of unifocal EG of the mandible occurring in a 4-year-old boy whose initial presentation led to confusion between osteomyelitis, primary bone tumour and lymphoma. A final diagnosis of EG was established after histopathological examination of the biopsy specimen.