Least (Calidris minutilla, n = 110) and Western (Calidris mauri, n = 37) sandpipers collected in Cuban wetlands were sexed by gonadal examination on dissection and used to assess the robustness of two morphometric methods commonly used to assign sex in shorebirds. Discriminant function analyses were performed and then tested by jackknife validation. The best discriminant function for Least Sandpiper included culmen and wing lengths and correctly classified 91% of the birds. Using culmen length, the discriminant function correctly sexed 97% of the Western Sandpiper. Sex ratio and morphometric estimates obtained through sexing Least and Western sandpipers by discriminant functions were not significantly different from the population sexed by gonadal examination on dissection. The range of the bill lengths used for sex determination of Least and Western sandpipers were then assessed by fitting the known-sex data. Classification accuracy of the bill length method was high for Western Sandpiper (95%), but was imprecise (44%) and female biased for Least Sandpiper. Consequently, a female biased sex ratio and under-estimation of male culmen length occurred for Least, but not Western, sandpipers classified by the bill length method. The findings suggest that sex determination based on the single measurement of culmen length is only accurate for Western Sandpiper, a species with high sexual size dimorphism. Linear measurements are also important for sex assignment in Least Sandpiper, but only using a discriminant function analysis approach.