The clinical implications of specific human papillomavirus (HPV) types in invasive cervical carcinomas are only beginning to be appreciated. In this series of 100 women with cervical cancers analyzed for the presence of HPVs 6, 11, 16, 18, and 31 by Southern blot hybridization, a more aggressive clinical behavior was demonstrated for tumors containing HPV 18 than for those with HPV 16 or those in which no HPV was identified. Among 69 stage Ib tumors, no significant differences were found in the size of tumor, presence of parametrial involvement, or lymph node metastasis among patients whose tumor contained HPV 16, HPV 18, or no HPV DNA; however, 45% of the women with HPV 18-containing tumors (five of 11) had recurrence, as compared with only 16% of those with HPV 16 (five of 31) during the 20-month mean follow-up period. This tendency for HPV 18-containing tumors to recur was seen with all histologic subtypes of cervical cancers and with all grades of tumor. In addition, patients with HPV 18-containing tumors were more likely to give a history of recent normal Papanicolaou smears than were those whose tumors contained HPV 16. Forty-four percent of women with HPV 18 in their tumors had a history of three class I Papanicolaou smears in the 3 years before the diagnosis of cancer, whereas a similar history was elicited in only 16% of those with HPV 16 in their tumors, suggesting that HPV 18-containing tumors might progress to invasion without a prolonged preinvasive period.