For a pair (f, g) of sequences of length ℓ whose terms are in {−1, 1}, Pursley and Sarwate established a lower bound on a combined measure of crosscorrelation and autocorrelation for f and g. They showed that the sum of the mean square crosscorrelation between f and g and the geometric mean of f 's mean square autocorrelation and g's mean square autocorrelation must be at least 1. For randomly selected binary sequences, this quantity is typically about 2. In this paper, we show that Pursley and Sarwate's bound is met precisely when (f, g) is a Golay complementary pair. This result generalizes to sequences whose terms are arbitrary complex numbers.