Seventy-nine patients with adenoid cystic carcinoma arising in salivary glands were studied to determine whether a correlation existed between the morphologic features of the tumor and the prognosis. Three histologic grades were established: Grade I, tumors with tubular and cribriform areas but without solid components; Grade II, cribriform tumors that were either pure or mixed with less than 30% of solid areas; and Grade III, tumors with a predominantly solid pattern. Cumulative survival rates at 15 years were 39%, 26%, and 5%, for Grades I, II, and III, respectively. Grade III tumors were larger, recurred frequently, and killed the patients within 4 years. Grade I lesions were smaller, were amenable to complete surgical excision, and had a protracted clinical course. Grade II tumors lay between the other two forms both clinically and pathologically. Other important prognostic features of the adenoid cystic carcinoma were its primary site, its presence or absence at surgical margins, and the anatomic structures it involved.