Histologic specimens from 61 cases of adenoid cystic carcinoma of the head and neck were reviewed in order to determine prognostic factors of this peculiar neoplasm. After the tumor was reviewed and classified according to several criteria, follow-up information, which was available in 54 cases, was analyzed and compared with each histological subgroup. As for the histologic pattern, the prognosis of adenoid cystic carcinoma with a solid pattern was worse than that without a solid pattern in respect of 5- and 10-year survival rates. However, there was no difference in 15-year survival between the two groups. Tumors with severe cell atypia showed more malignant behavior than those with moderate or mild atypia (p less than 0.001). Increased mitotic activity of more than two cells in mitosis per high power field was also found to be a sign of poor prognosis (p less than 0.001). Presence of perineural invasion was not correlated with the final outcome of the disease. Cell atypia and mitotic activity as well as the histologic pattern should be evaluated for assessing the degree of malignancy of adenoid cystic carcinoma.