A 16-year-old boy presented with a short history of pain of the lower spine, fatigue and intermitting febrile episodes. T2-weighted magnetic resonance imaging of the spine revealed compression fractures of Th12, L1, L5 and a heterogeneous enhancement of the vertebral spine (top left); T1-weighted imaging demonstrated a homogeneous suppression of the bone marrow fat signal. In the light of these findings, a haematological malignancy was suspected and the patient was admitted to our department. White blood cell count, haemoglobin concentration and platelet count were within the normal ranges, but some myeloblasts and promyelocytes were seen. The lactate dehydrogenase level was elevated to 2529 U ⁄ l. May– Grünwald–Giemsa (MGG)-stained bone marrow smears showed infiltration by primitive cells. These contained round or oval, occasionally lobulated nuclei with often clearly visible nucleoli, a high N ⁄C ratio and sometimes vacuoles within a basophilic cytoplasm. Multinucleated forms were also discernible (top centre). Immunostaining was positive for desmin and vimentin, whereas cytokeratin and CD61 were not detectable. Flow cytometry demonstrated CD56 expression but no other lymphoid or myeloid antigens. Cytogenetic studies showed a tetraploid karyotype with a translocation t(2;13)(q35;q14) in 10 out of 13 metaphases, confirming the provisional diagnosis of bone marrow infiltration by alveolar rhabdomyosarcoma. The primary tumour was found to be a subcutaneous plantar mass on the left foot. Ultrasound examination demonstrated a hypoechoic and inhomogeneous tumour of 2Æ5 cm in diameter with cystic areas (top right). Cytological examination showed tumour cells similar to those detected in the bone marrow when stained with MGG (bottom left) and for desmin (bottom right). The patient was treated with chemotherapy according to the German Soft Tissue Sarcoma Study Group CWS 96 protocol but died 2 years after diagnosis due to progressive disease. Bone marrow metastasis is particularly common in alveolar rhabdomyosarcoma, which is usually diagnosed in older children or younger adults, and may mimic an acute haematological neoplasia.