The intraosseous mucoepidermoid carcinoma is a rare lesion that frequently affects the posterior region of the mandible. This case reports a multilocular osteolytic radiolucency with two years of evolution, that expanded and perforated the cortical bone, with irregular and indefinite margins, that extended from the mandibular angle to the ascendant ramus, with cutaneous ulceration, detected in a 51 years-old male. An incisional biopsy was performed and confirmed the diagnosis of low-grade intraosseous mucoepidermoid carcinoma. The patient was submitted to partial mandibulectomy, neck dissection and post-operative radiotherapy. In three years of follow-up, there was no evidence of tumor recurrence. This case report reinforces that even a low-grade intraosseous mandibular mucoepidermoid carcinoma tends to expand and to perforate the bone cortical, infiltrating to adjacent soft tissues, in long time of evolution.