Incidence and size variability of the metaconule, an accessory maxillary molar cusp, is analyzed in a series of 1,217 living Melanesians. The range of morphologic variation is quantified on a six-grade ordinal scale developed to standardize observations. Total incidence of the metaconule decreases along a mesial-to-distal gradient, while mean size and size variability increase from M1 to M3. So, while the trait is less common on distal molars, it is on average larger. Estimation of the additive genetic component is 65% for the first molar but only 15% for the second. Trait incidence and heritability estimates are generally higher for females indicating the need for separate analysis by sex.