Whereas benign leiomyoma of the uterus (fibroid) is very common, malignant degeneration of such fibroids to leiomyosarcoma is rare. Anatomical imaging with CT or MRI cannot differentiate between larger leiomyoma and leiomyosarcoma. Imaging with 18F-FDG PET/CT can be helpful in differentiating the two. High-grade 18F-FDG uptake in uterine fibroids is suspected and warrants surgical excision for further evaluation. We present such as case of a 42-year-old premenopausal woman where 18F-FDG PET/CT helped in making the diagnosis of malignant degeneration of uterine fibroid.