An organic light emitting display includes a plurality of pixels and a compensation unit. Each of the pixels includes a driving transistor to control an amount of current supplied to a corresponding organic light emitting diode. The compensation unit is coupled to the pixels by data lines and includes at least one sensing unit. The sensing unit extracts threshold voltage information from the pixels corresponding to respective driving transistors. The sensing unit receives noise currents from a plurality of data lines, offset the noise currents, and extracts the threshold voltage information after offset of the noise currents.