Cervical neuroendocrine carcinomas are rare, aggressive tumors and their immunohistochemical features and clonal relationship to coexisting tumors are incompletely described. Twenty-eight cases were identified (17 small cell, 9 large cell, and 2 mixed), 10 of which had an invasive squamous or adenocarcinoma component. Staining for synaptophysin, chromogranin A, TTF1, c-kit, CD44, and p16 was performed. Analyses for loss of heterozygosity (LOH) at 5 polymorphic microsatellite markers (D3S1300, D9S171, D11S914, D13S319, and TP53) and X-chromosome inactivation were performed. Of 17 cases with available blocks, 13 (76%) were synaptophysin+, 8 (47%) were chromogranin A+, 8 (47%) were TTF1+, 7 (41%) were c-kit+, and 6 (35%) were CD44+. Strong patchy or strong diffuse p16 staining was seen in all cases. LOH and X-chromosome inactivation analysis were performed for 17 cases, 8 of which had a coexisting squamous or adenocarcinoma component. Five of the 8 (63%) cases with 2 components showed allelic loss in both components. All 5 of these cases demonstrated identical LOH between the neuroendocrine and squamous or adenocarcinoma components. Nonrandom X-chromosome inactivation was seen in the neuroendocrine and other components in 4 of the 8 cases. In all 4 cases the pattern of inactivation was identical between the 2 components. Cervical neuroendocrine carcinomas have features similar to other extrapulmonary neuroendocrine carcinomas, including expression of TTF1, c-kit, and CD44. Consistent staining for p16 is also seen. Concordant genetic alterations support common clonal origin for neuroendocrine carcinomas with a coexisting squamous or adenocarcinoma component.