Although the radial forearm flap has become a workhorse for the reconstructive surgeon, it has some known disadvantages, especially relating to donor area complications. The authors present a serious but rare complication of the radial forearm donor site. Osteomyelitis of the radius at the flap donor site was observed in a 48-year-old man 5 weeks after flap surgery. Although the flap was raised fasciocutaneously without a bony portion, infection of the radius was determined. The infection was successfully treated with surgical debridement and simultaneous administration of a proper antibiotic regimen. One should keep in mind that osteomyelitis of the radius may be encountered as one of the serious donor site complications of the radial forearm flap that may have detrimental effects on hand functions.