The finger print patterns of an unselected series of same-sexed sets of triplets have been analysed with respect to qualitative and quantitative characteristics. The material comprised nine trizygotic, 28 dizygotic, 16 monozygotic and one un-classifiable, probably trizygotic sets. Comparisons between the various zygosity types and between each of these and the general population showed that monozygotic triplets from monozygotic sets had a significantly lower proportion of arches than any other group. Monozygotic triplets from dizygotic sets and the two groups of dizygotic triplets presented only minor deviations from one another and from the population with regard to qualitative characteristics. No indications of a high frequency of mirror-imaging in monozygotic triplets were observed. The mean of the total ridge-count was higher and the variance lower in monozygotic triplets from monozygotic male sets than in monozygotic triplets from dizygotic male sets. The former group also presented less similarity between the members of a set with respect to total ridge-count. Most of these qualitative pecularities were only seen in males which makes it less likely that they are related to the special conditions connected with the origin of monozygotic sets of triplets. The only more general difference between most groups of triplets and the population was a lower variance of total ridge-counts; this may possibly be associated with the unusual intrauterine conditions of triplet pregnancies. In the evaluation of triplet zygosity, based on finger print examinations, it seems safe to use the empirical odds values obtained from twin materials in the calculation of the probability of monozygosity.