Lymphoblastic lymphoma (LL) of the B cell type is uncommon, and extranodal presentation is even rarer. It is difficult to suspect this diagnosis without clinically obvious lymph nodal mass or bone marrow involvement. A 3-year-old girl presented with progressive pain and swelling of the right knee joint of 3 months duration. Radiograph revealed expansile lytic lesion at the supracondylar area of the right femur; with pathological fracture and multiple lytic areas in both femora. She neither had lymphadenopathy nor organomegaly. Her blood counts, peripheral smear examination and bone marrow examination were normal. Right supracondylar biopsy revealed diagnosis of a precursor B cell LL. Computerized tomography scan revealed a hypodense, poorly enhancing lesion in the left adnexal region. Although rare, precursor B-cell LL may present with extensive bone lesions. Early and accurate diagnosis of this entity is very important due to its high cure rates.