The aim of this study was to evaluate F-FDG PET/CT findings of malignant nonepithelial prostate tumors and their correlation with MRI and CT images. FDG PET/CT findings were reviewed in 12 patients with malignant nonepithelial prostate tumor confirmed by pathology. The location, size, SUVmax, pathologic findings, and available MRI and CT images of the tumors were reviewed. Of the 12 patients (mean age, 41 years; age range, 19-66 years), 9 had normal prostate-specific antigen levels. The mean size of the tumors was 7.1 cm in diameter ranging from 4.6 to 10.5 cm. All the tumors showed increased metabolic activity with mean SUVmax of 17.5 ranging from 3.6 to 46.8. The high-grade malignant tumors tended to show higher FDG uptake, whereas the intermediate-grade and low-grade malignant ones tended to show lower FDG uptake. Seven tumors had local invasion or distant metastases. Lung was the most common metastatic site. On MRI, the tumors showed well-circumscribed or ill-circumscribed margins with inhomogeneous enhancement. On CT, the tumors showed hypodensity with slight to moderate enhancement. The malignant nonepithelial prostate tumors tended to have large sizes at presentation, have high FDG uptake, and affect a younger population with normal prostate-specific antigen levels. FDG PET/CT may be useful for the assessment of tumor grade and for detecting the distant metastases, whereas the MRI or enhanced CT may be more helpful for describing the relationship between the tumor and adjacent structures.