We analyze the error performance of a space-time coding system using M transmit and N receive antennas with imperfect channel estimation in Rayleigh fading. A least-squares estimate of the channel matrix is obtained by using a sequence of pilot code symbols. The estimate is found to be perturbed by an M/spl times/N perturbation matrix with correlated zero-mean circular Gaussian entries. An N/spl times/L code matrix is used to transmit N/spl times/1 code vectors over L symbol intervals. Using the characteristic function of the decision variable,. we derive a closed-form expression for the pairwise error probability. Numerical results show that the degradation in performance due to imperfect channel estimation can be compensated by increasing the number of receive antennas.