The aim of this study was to describe the size dimorphism in adult Eurasian Coots (Fulica atra). Appropriate discriminant functions to allow efficient sex determination on the basis of morphological measurements were developed. Breeding Eurasian Coots (n = 55) were captured from the urban population in central Poland. Eight measurements were collected from each individual, and all individuals were molecularly sexed. Head length and wing length yielded the highest discriminatory power among the collected measurements, with males larger than females. Using a jackknife procedure, a combination of these two measurements correctly sexed approximately 95% of Eurasian Coot individuals. The discriminant functions developed here could be a reliable alternative to molecular sexing techniques in the Eurasian Coot.