Lower female genital tract tumors with adenoid cystic differentiation are rare, and data on their relationship with high-risk human papillomavirus (HPV) are limited. Here we report the clinicopathologic features from a case series. Tumors with adenoid cystic differentiation, either pure or as part of a carcinoma with mixed differentiation, arising in the lower female genital tract were evaluated by means of immunohistochemical analysis for p16 expression and in situ hybridization using 1 or more probes for high-risk HPV (a high-risk probe covering multiple types, a wide-spectrum probe, and separate type-specific probes for HPV16 and HPV18) and when possible by polymerase chain reaction for high-risk HPV. Six cervical carcinomas with adenoid cystic differentiation admixed with various combinations of at least 1 other pattern of differentiation, including adenoid basal tumor (epithelioma and/or carcinoma), squamous cell carcinoma (basaloid or keratinizing), and small cell carcinoma were identified in patients ranging in age from 50 to 86 years (mean, 73 y; median, 76 y). All of these tumors were characterized by diffuse p16 expression. High-risk HPV was detected in 5 of 6 tested cases: 4 cases by in situ hybridization (all positive for HPV-wide-spectrum and HPV16) and 1 by polymerase chain reaction (HPV45). Seven pure adenoid cystic carcinomas (6 vulvar and 1 cervical) were identified in patients ranging in age from 27 to 74 years (mean, 48 y; median, 48 y). All of these tumors were characterized by variable p16 expression ranging from very limited to more extensive but never diffuse. No high-risk HPV was detected in any of these pure tumors. Lower female genital tract carcinomas with adenoid cystic differentiation appear to comprise 2 pathogenetically distinct groups. Cervical carcinomas with mixed differentiation, including adenoid cystic, adenoid basal, squamous, and small cell components, are etiologically related to high-risk HPV and can be identified by diffuse p16 expression. Pure vulvar and cervical adenoid cystic carcinomas appear to be unrelated to high-risk HPV and are distinguished from the mixed carcinomas by nondiffuse p16 expression.