In this contribution, we provide an exact bit error rate (BER) analysis of orthogonal space-time block codes over arbitrarily distributed (possibly correlated) block fading channels with imperfect channel estimation. The transmitted symbols belong to a PAM or QAM signal constellation. With N-t and N-r denoting the number of transmit and receive antennas, respectively, the resulting average BER can easily be written as an expectation over 4N(t)N® real-valued random variables, but the computation time needed for its numerical evaluation increases exponentially with N-t and N-r. We provide a methodology that allows an efficient numerical evaluation of the exact BER with a computation time that is essentially independent of NtNr and the signal-to-noise ratio.