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The purpose of this investigation is to express the similarity of the cranio­facial shape among relatives in terms of a single parameter and to deter­mine to what extent the variability of hone morphology is genetically determined. To quantify the facial similarity between any two subjects, diagrams plotted from their lateral cephlograms are so oriented that the distance from each point on one to the corresponding point on the other is minimized. To achieve this fit, it is necessary, first, to center one diagram on the other; second, to reduce both to the same size; third, to rotate one on the other until the best fit is obtained; and last, to measure the best fit. The data consists of measurements from MZ and DZ twins, as well as siblings and parents. The average dissimilarity is computed in each group and compared. The results indicate that this method can he used to estimate the environmental and genetic effects on variation of the craniofacial shape.