Background: Malignant mixed Müllerian tumors (MMMTs) are aggressive tumors arising in the female lower genital tract and characterized by the presence of both a malignant epithelial and a mesenchymal component. Here, we report a case of an MMMT of the uterine corpus with an extensive squamous-cell carcinomatous component processed by liquid-based cytology (LBC). Case Report: An 84-year-old woman with a prior history of anal squamous-cell carcinoma, who complained of vaginal bleeding, was discovered to have a mass protruding from the uterine cervix. A Papanicolaou (Pap) test was performed and the LBC (ThinPrep) preparation showed a background of neutrophils and cellular debris. Atypical cells were identified that presented with hyperchromatic nuclei, nuclear membrane irregularities, multinucleation and abundant cytoplasm with focal keratinization. Scattered nucleolated malignant elements were also identified. The cytological diagnosis resulted in ‘suspicious for squamous-cell carcinoma', favoring primary cervical carcinoma rather than extracervical (anal) carcinoma. The histological examination showed that it was an MMMT with an extensive squamous-cell carcinomatous component. Conclusion: This case illustrates the potential diagnostic pitfall of MMMTs with extensive squamous-cell carcinomatous components in LBC Pap smears. Cytopathologists should keep in mind this diagnostic possibility in postmenopausal women who experience vaginal bleeding or spotting.