OBJECTIVE: To highlight the impact of the immunohistochemistry in the diagnosis and behavior in rhabdomyosarcoma of infrasecular tank. CASE REPORT: L.C.D., masculine, 5 years. Main complaint: "swell in the face". History of the current disease: Mother tells that she has one lesser month presented tumor in left hemiface and fever surveyed of 38,5°C. Ponderal loss of approximately 5 kg in the period, prostration, dysphagia for solids and liquids and irritability. To the examination: Tumor hardened in the left parotid region, adhered the neighboring structures, asymmetry of face and ipsilateral cervic lymphonodomegaly. Oropharynx with important bulging of the left palate fibrous, speaks sultry and drooling. Computerized Tomography of head and neck: tumor occupying predominantly the left infrasecular tank, with great area of necrosis. Carried through transoral incisional biopsy for transpalatal access under general anesthesia and tracheotomy of urgency. Biopsy for congelation disclosed malignant neoplasias little differentiated. Immunohistochemistry, embryonic rhabdomyosarcoma with positivity for desmin. Directed for chemotherapy treatment. CONCLUSION: Rhabdomyosarcoma is the malignant tumor of soft parts more common in infancy, aggressive, being situated preferential in the head and neck. It presents varied biological clinical behavior, having to receive multimodal therapy individualize more precociously possible. The immunohistochemistry, when applied well, is a useful complementary diagnostic method and contributes basically in the therapeutical behaviors. When used in way directed to the main distinguishing diagnostic, the technique presents a relation high cost benefit.