The construction of a class of balanced binary sequences with optimal autocorrelation properties is described. Given any odd prime

and any positive integer

, a balanced

binary sequence of length

whose cyclic autocorrelation function

satisfies

, and, for

or

when

is odd, and

or

when

is even is constructed. Optimality is proved by showing that every balanced binary sequence has at least two distinct out-of-phase correlation values which are at least as large as those obtained here.