BACKGROUND: Standard treatment for placental site trophoblastic tumor is hysterectomy. This may be unacceptable to women desiring fertility. Cells aberrant in placental site trophoblastic tumor display an ability to invade normal tissue while evading the immune system. CASE: We present a case of a 23-year-old woman with stage I placental site trophoblastic tumor who declined hysterectomy. Tumor assay for program cell death-ligand 1 staining was performed and suggestive of an immune-responsive tumor. The patient initiated intravenous pembrolizumab 200 mg every 2 weeks, and by cycle 3 her β-hCG level fell to undetectable. She subsequently conceived and went on to have an uncomplicated term vaginal birth after cesarean. At 6 weeks postpartum, she remained without evidence of disease. CONCLUSION: Immunotherapy can eliminate early program cell death-ligand 1-positive placental site trophoblastic tumor with subsequent normal pregnancy.