Summary: We performed a prospective study using both FRAX and computed tomography to screen for osteoporosis in men undergoing radiation for prostate cancer. We found that implementing routine computed tomography (CT)-based screening was feasible in the setting of a prospective study, but the yield of osteoporosis identification was low in this population. Purpose: Men with prostate cancer (PCa) are at increased risk of hip fracture for multiple reasons. Estimation of hip fracture risk with the FRAX tool is currently recommended, but FRAX alone may not identify a portion of men with osteoporosis. We hypothesized that adding bone mineral density (BMD) screening using CT to FRAX is feasible and would identify more men with osteoporosis. Methods: Men with PCa scheduled to undergo CT simulation for radiation treatment were enrolled in a single-arm prospective study. The mean attenuation of the mid-L5 vertebral body trabecular bone (L5CT) was calculated on a single slice using the radiation simulation CT scan. The 10-year risk of hip fracture was calculated using the FRAX tool. Dual energy X-ray absorptiometry (DXA) was performed for men whose L5CT measurement was less than 130 Hounsfield units (HU). Results: A total of 98 eligible men were enrolled and underwent FRAX and CT screening. The median 10-year risk of hip fracture was 1.1% and exceeded 3% in 16 cases; the median L5CT was 162.28 HU (range 55.6–526.1 HU). DXA scan was completed in 15 men who had L5CT < 130 HU but 10-year calculated hip fracture risk < 3%, 1 of whom was found to have osteoporosis (T-score ≤ −2.5). Conclusions: Implementing CT-based BMD screening was feasible in the setting of a prospective study for men receiving radiation for PCa, but fewer cases than anticipated of osteoporosis were identified.