A genetical analysis of variation in finger ridge counts of 221 pairs of twins and 80 pairs of opposite sex siblings has been carried out. Negative regression of DZ and sibling pair variances on pair means suggests the action of non-additive genes or unequal gene frequencies tending to increase finger ridge counts. Negative skewness of the distributions supports this view. While models including dominance or epistasis are not a significant improvement over purely additive genetic models, it is regarded as important that large and positive values of non-additive genetic variance are estimated. The evolutionary importance of dominance and epistasis for greater finger ridge counts is discussed.