Endometriosis is a common medical condition with rare reports of FDG findings in the scintigraphic literature. We present a 36-year-old premenopausal woman with a left ovarian endometrioma that presents a photopenic defect on the FDG-PET scan. The case demonstrates the value of FDG-PET scan in differentiating benign from malignancy in surveying ovarian lesions. The literature associated with endometriomas and FDG-PET scan, and the factors that may contribute to FDG-PET finding of endometriomas are discussed.