Over a 14 year period, we determined offspring sex ratios in a population of Savannah Sparrows (Passerculus sandwichensis) breeding on Kent Island, an isolated 80 ha island in the Bay of Fundy, New Brunswick, Canada, based on morphological measurements of 318 independent juveniles and 361 returning adults of known parentage. The mean annual offspring sex ratio was exactly 1.00 (±0.23, range= 0.61–1.41, n = 14). In no year did offspring sex ratio deviate significantly from 50:50, regardless of the sex ratio of breeding adults. Offspring sex ratio did not vary as a function of the timing of breeding, maternal or paternal age, or parental mating status (monogamy vs. polygamy). Overall, our data provide strong support for 50:50 offspring sex ratios at the population level (Fisher 1930), but no support for the notion of adaptive modification of offspring sex ratios by individuals (Trivers and Willard 1973).