Discriminant analysis was used to identify the sexes of fledglings and yearlings in the Magellanic Penguin (Spheniscus magellanicus). Eleven morphometric measurements were recorded in a sample of 102 fledglings and 140 yearlings from the breeding stock at Punta Clara, Chubut, Argentina. Total (body) length and bill depth were the most useful variables for discriminating between age classes, followed by length of the middle toe and bill length. Yearling, besides being distinguishable by plumage, were invariably bigger than fledglings. For distinguishing the sexes among yearlings, bill depth and tarsus length proved useful; 95.7% of cases were correctly classified (Chi square, p <0.001). In fledglings, two variables, bill depth and length of middle toe correctly classified 93.1% of cases (Chi square p <0.001). This method provides a simple and objective way of identifying the sex of the Magellanic Penguin eliminating the subjective factors and placing emphasis on the more significant morphological characters.