OBJECTIVE To investigate the prevalence and oncologic outcomes of patients with multiple primary malignant tumors (MPMT) with gynecologic cancer. METHODS This retrospective study included 1929 patients diagnosed with gynecologic cancer at a tertiary medical center between August 2005 and April 2021. The clinical data included cancer location, age at primary malignancy diagnosis, interval between primary and secondary cancer, stage of cancer, family history of cancer, genetic testing, dates of last follow-up, recurrence, and death. RESULTS The prevalence of MPMT with gynecologic cancer in patients was 8.6% and the mean diagnostic period between primary and secondary cancer was 60 months. Furthermore, 20 of the 165 patients with MPMT had multiple primary gynecologic cancers (MPGC), whereas 145 had gynecologic cancer coexisting with non-gynecologic cancer (GNC). Endometrial-ovarian cancer (60%) was the most common coexisting cancer in the MPGC group, whereas the most common non-gynecologic cancer in the GNC group was breast cancer (34.5%). There were 48 patients with synchronous cancer and 117 patients with metachronous cancer. The incidence of synchronous cancer was higher in the MPGC group than in the GNC group (p = 0.037). Significantly more patients had early-stage ovarian cancer in the MPGC group than in the GNC group (p = 0.031). The overall recurrence and mortality rates were 15.8% and 8.5%, respectively, in patients with MPMT. CONCLUSIONS Synchronous cancer incidence was significantly higher in the MPGC than in the GNC group. Early-stage ovarian cancer was more highly diagnosed in patients with MPGC than in those with GNC. A systematic examination after primary cancer diagnosis could facilitate the early diagnosis of secondary primary malignancy, thereby improving patient prognosis.