White-tailed deer were introduced to Finland in 1934 from Minnesota, North America. The population has expanded and is now an important wildlife species, managed through hunting. We determined the age of 451 individuals harvested in the 2012 hunting season. Hunters measured their body mass after slaughter and we measured the dimensions of the lower jaw (in both sexes) as well as skull dimensions and antler scores (in males). The sample indicated a deficit of older males in the population. Females seem to gain their size at the age of two while males continue to increase their body size and that of skeletal traits until the age of four. The size traits measured were similar to those in the North American studies. Based on population growth patterns and introduction history, the white-tailed deer population is performing well in Finland but the potentially skewed sex-specific age distribution warrants further attention.