Experimental and animal studies, as well as genetic mutations in man, have indicated that the development of dentition is under the control of several genes. So far, mutations in MSX1 and PAX9 have been associated with dominantly inherited forms of human tooth agenesis that mainly involve posterior teeth. We identified a large kindred with several individuals affected with molar oligodontia that was transmitted as an isolated autosomal-dominant trait. Two-point linkage analysis using DNA from the family and polymorphic marker D14S288 in chromosome 14q12 produced a maximum lod score of 2.29 at theta = 0.1. Direct sequencing of exons 2 to 4 of PAX9 revealed a cytosine insertion mutation at nucleotide 793, leading to a premature termination of translation at aa 315. Our results support the conclusion that molar oligodontia is due to allelic heterogeneity in PAX9, and these data further corroborate the role of PAX9 as an important regulator of molar development.