A new high dynamic range CMOS x-ray detector is described. This sensor was designed specifically for x-ray imaging as opposed to the common approach of modifying a 3T optical sensor design. This allowed for a highly linear, wide dynamic range operation that has otherwise been a major drawback of CMOS x-ray detectors. The design is scalable from small tiles to large wafer-scale imagers fabricated on 300mm wafers. The performance of such a detector built using a 9.4cm x 9.4cm tile is reported. The pixel size of this detector is 76 μm and it can be operated in the native resolution or 2x2 binned mode. Measurements were performed with a thallium-doped cesium iodide (CsI(Tl)) scintillator deposited on a reflective aluminum substrate. The imager was operated at 30 frames/second. The linearity, dynamic range, sensitivity, MTF, NPS and DQE at RQA5 were measured using the standard protocols. Linearity was measured to be better than 0.2%. Using 600 μm CsI(Tl) scintillator, the maximum linear dose was 9 μGy with high gain and 56 μGy with low gain settings. This is comparable to conventional amorphous silicon flat panel detectors. The MTF is dominated by the scintillator and is 58% at 1 lp/mm and 28% at 2 lp/mm. The DQE is 70% at 0 lp/mm and 12% at the Nyquist frequency of 6.6 lp/mm. The high resolution combined with the large dynamic range and excellent DQE makes this CMOS detector particularly suitable for dynamic imaging including fluoroscopy, angiography and conebeam CT.