Rhabdomyosarcoma of the diaphragm is a very rare entity, especially in childhood. A case of a 4-year-old girl is reported. The mass extended completely into the abdominal cavity, causing problems in differential diagnosis with other abdominal masses. Dimensions, structure and limits of the mass had been outlined by several examinations (IVP, sonography, CT, angiography), but its actual nature could not be shown, so that a surgical exploration was needed. A pedunculated, well-capsulated mass, arising from the left diaphragmatic portion, was found. A complete excision could be performed and histologic findings were compatible with rhabdomyosarcoma of the diaphragm.