An organic light emitting display capable of reducing power consumption and controlling brightness in response to the intensities of peripheral light. The organic light emitting display includes a data driver for supplying data signals to data lines, a scan driver for sequentially supplying scan signals to scan lines and sequentially supplying emission control signals to emission control lines, a display region including a plurality of pixels for receiving the data signals, the scan signals and the emission control signals to display images and a brightness controller for controlling the brightness of the display region. The brightness controller controls the brightness of the display region in response to the data of one frame and the intensities of peripheral light. This system reduces power consumption, controls the brightness of the display region in response to the intensities of the peripheral light and improves the contrast of the display region.