We report results of a retrospective study of 12 cases of adenoid cystic carcinoma (ACC) in the parotid gland. Local pain was often observed in ACC among other malignant parotid tumors. Although fine-needle aspiration cytology (FNA) was not effective for preoperative diagnosis, frozen section diagnosis (FS) during surgery showed excellent results. Cases with T3 or T4 underwent total or enlarged parotidectomy, but, often showed positive surgical margins. Postoperative radiation therapy seemed useful in these cases and the 5-and 10-year disease-specific survivals in these 12 cases were 90.0% and 80.8%. These compare favorably with other reports in the literature. All 12 cases showed NO and no cervical relapse with or without neck dissection, indicating little effectiveness in prophylactic neck dissection. Tumor size, positive surgical margins, and perineural invasion are risk factors for this tumor as mention previously. Patients with perineural invasion, especially preoperative facial nerve palsy (T4a), are more likely to fail than those with two other factors, so, it seems conceivable for cases of T4a to undergo more positive treatment with surgery and postoperative radiation.