Lately, STK11 adnexal tumors have been described in patients with Peutz-Jeghers syndrome (PJS), showing overlap with other adnexal tumors, especially female adnexal tumor of probable Wolffian origin (FATWO). To date, there is no documentation of this tumor from the Indian subcontinent. A 25-year-old female with mucocutaneous pigmented macules presented with acute abdominal pain along with a family history of surgical resection for gastrointestinal polyps in her mother and sister. Imaging revealed a well-defined, cystic right adnexal mass, distinct from the ovary, measuring 4.1 cm. Her colonoscopic examination was unremarkable. She underwent paraovarian cystectomy. Histopathological examination revealed a tumor composed of epithelioid cells arranged in various growth patterns with mild nuclear atypia. Immunohistochemically, the tumor cells were positive for pan-keratin, calretinin, CD10, FOXL2, and androgen receptor, the latter in 50% of the tumor cell nuclei. Initially, a diagnosis of FATWO was considered. Targeted next-generation sequencing revealed a pathogenic STK11 exon 4 frameshift mutation (c. 574dup), which was subsequently confirmed as a germline alteration on peripheral blood testing by Sanger sequencing, thereby establishing the diagnosis of an STK11 tumor with PJS. The differential diagnoses of this tumor and the judicious application of immunohistochemical stains, along with genetic testing (including high-throughput molecular testing in a clinical context) for an exact diagnosis, are discussed herein. A literature review including the molecular results of this rare tumor is also presented.