The expression of bilateral non-metric traits is rarely symmetrical. This simple observation has generated a large amount of scientific literature over the years. The present article defines the concept of fluctuating asymmetry which characterises the expression of human skeletal non-metric traits, and evokes the controversial role of genetics in the amount of asymmetry encountered, as well as the different types of environmental factors which have been thought to play a role in bilateral trait expression. Two simple procedures are proposed in order to arrive at an unbiased estimation of the degree of fluctuating asymmetry present within different samples. Finally, the "individual count" method is recommended, based on the basic premise that an individual bas only a single genotype for any specific trait, and should therefore be classified in only one phenotypic category.