We report visible light and X-ray imagers on lightweight and mechanically flexible plastic substrates. The process involves solution processing of organic photodetectors on top of an active-matrix backplane consisting of carbon nanotube thin-film transistors. The system takes advantage of the high mobility of nanotube transistors for low operating voltages and efficient light absorption of organic bulk-heterojunctions for high imaging sensitivity. With this highly scalable process scheme, 18 × 18 pixel-array flexible imagers (physical size of 2 cm × 1.5 cm) with high performance are successfully demonstrated. In addition, as the absorption peak of the adopted organic photodiodes covers the green band of the light spectrum, X-ray imaging is readily demonstrated by placing a scintillator film on top of the flexible imagers.