This paper considers the performance analysis of space-time trellis codes over quasistatic Rayleigh fading channels. We present three methods to calculate the frame error rate (FER) of such codes. The first is based on the union bound using the exact pair wise error probability (PEP). The second method is a generalization of the PEP-based union bound, employing the exact FER of orthogonal subcodes. The third method uses the technique of limiting the conditional union bound before averaging over channel coefficients. Numerical results show that employing the exact orthogonal subcode FER improves the union bound significantly. Limiting before averaging, however, provides the closest approximation to FER among these three methods.