A 46-year-old women was examined for severe constipation. Pelvic examination revealed a large pelvic mass extending to the level of the umbilicus. Computed tomography showed a large multicystic, septated mass in the pelvis and a small amount of fluid in the cul de sac. In addition, multiple ill-defined, mixed-attenuation hepatic lesions were identified. A malignant ovarian neoplasm with liver metastases was considered, so the pelvic mass was resected. Interestingly, histopathologic analysis revealed malignant struma ovarii of the follicular type. Biopsy of the liver lesions confirmed metastatic disease with similar histopathologic findings. All thyroid laboratory values were in the normal range. The patient then had a total thyroidectomy to optimize thyroid ablation therapy with I-131. This revealed a small follicular adenoma but no evidence of cancer. An I-131 whole-body scan was performed and showed uptake in multiple functioning liver metastases.