Introduction: Rhabdomyosarcoma is the most common soft tissue sarcoma in patients under 25 years of age. The occurrence of mandibular rhabdomyosarcoma in a pregnant woman is rare with an incidence of 0.07 to 0.1 and the literature describes one case per 1000 deliveries. Only biopsy and histological examination make a definitive diagnosis. Treatment is based on a combination of chemoradiation and surgery. Objectives: To describe the diagnostic and therapeutic aspects of mandibular rhabdomyosarcoma in pregnant women. Observation: It was a 19-year-old patient who had consulted for left mandibular swelling evolving over 28 weeks. A morphological assessment had been requested but being almost full-term, the patient chose to let her pregnancy progress. She was seen again after delivery with a swelling that had tripled in volume with abundant bleeding on the alteration of the general condition. The imaging concluded that there was a large osteolytic mass of the mandible. The biopsy performed came back in favor of an infiltrating pleomorphic rhabdomyosarcoma. Treatment consisted of radiation therapy followed by surgery. The evolution was marked by the death of the patient after 01 month of radiotherapy. Conclusion: Rhabdomyosarcoma is an aggressive malignant tumor that most often affects subjects under 25 years of age and its appearance in pregnant women is rare.