Patients with Peutz-Jeghers syndrome (PJS) have a risk of complicating malignant tumors, including cancer of the uterine cervix. Mutations in the STK11 gene have been identified as being responsible for PJS. However, the genotype-phenotype correlation in PJS is poorly understood, especially with respect to malignant tumors. Here, we report a detailed analysis of a case of a cervical tumor in a PJS patient showing a large genomic deletion in exon 1 of STK11 without human papillomavirus infection. Histological examination revealed a complex histology consisting of three components: lobular endocervical gland hyperplasia (LEGH), minimal deviation adenocarcinoma (MDA) and mucinous adenocarcinoma. Immunohistochemistry for STK11 was positive in the LEGH and MDA components, while that of the mucinous adenocarcinoma stained very faintly. These findings support a close relationship among LEGH, MDA and mucinous adenocarcinoma and imply that inactivation of STK11 may occur during progression from MDA to mucinous adenocarcinoma.