We evaluated how well observers in a helicopter classed male white-tailed deer (Odocoileus virginianus) into groups ≤3.5 or ≥4.5 years old. Resightings of individually marked anti previously aged deer on 2 southern Texas ranches were used for evaluation during repeated helicopter surveys from 1986 to 1988. Classifications of marked males were at least ≥90% correct on 11 of 14 flights on 1 ranch and 6 of 14 on the other. Although accuracy was acceptable on many flights, some flights gave inaccurate estimates (> 10% misclassified) of male composition. Because managers make only a single, annual helicopter flight, we recommend male classifications made during helicopter counts be used as trend data and be evaluated over a number of years. Managers should avoid using male composition data from individual flights in calculations of harvest rate for a particular age class.