Between 1960 and 1989 1538 patients were treated with initial radiation therapy for FIGO Stage IB squamous cell carcinoma (SCC) of the cervix and 229 patients were treated for Stage IB adenocarcinoma (AC). The overall 5-year survival rates for patients with SCC and AC were 81 and 72%, respectively (P < 0.01). Patients with AC more often had a maximum cervical diameter < 4 cm than those with SCC (53% versus 47%). For 903 patients with tumors > or = 4 cm, 73% of those with SCC survived > or = 5 years compared with only 59% of those with AC (P < 0.01). Although there was no significant difference in the rate of pelvic disease recurrence for patients with AC or SCC tumors > or = 4 cm (17% versus 13%, P = 0.16), the rate of distant metastases was greater for patients with AC (37% vs 21%, P < 0.01). For patients with tumors > or = 4 cm, prognosis was strongly correlated with tumor size (P < 0.01) and lymphangiogram findings (P < 0.01) but not with age (P = 0.58) or tumor morphology (exophytic versus endocervical) (P = 0.33); a trend toward better survival in 165 patients who underwent adjuvant hysterectomy (78% versus 71%) was not significant (P = 0.09). Multivariate analysis confirmed a highly significant independent association between histology and survival; patients with tumors > or = 4 cm in diameter that were AC had an estimated risk of death 1.9 times that of patients with SCC (P < 0.01). These results provide strong evidence that patients with AC of the cervix have a poorer prognosis than those with SCC of similar stage and tumor diameter, reflecting primarily a higher rate of distant metastases in patients with AC.