The purpose of the study was to estimate familial correlations and heritability to evaluate familial aggregation patterns of maxillary midline diastemas. The sample consisted of 30 extended families: 15 black, 14 white, and 1 mixed race. A single ascertainment scheme was adopted to collect the sample. Family data were collected with a 7-question survey. In all, the sample of 430 subjects consisted of 220 females, 210 males, 99 nuclear families, 534 sibling pairs, 422 avuncular pairs, 318 grandparent pairs, and 27 cousin pairs. Families were stratified by race to avoid any bias. The mixed-race family was excluded from the analysis. Data were analyzed using the program REGC in the Statistical Analysis for Genetic Epidemiology (S.A.G.E., Case Western Reserve University, Cleveland, Ohio) software. Heritability was found to be 0.32 +/- 0.14 in the white sample and 0.04 +/- 0.16 in the black sample. The preliminary results suggest a possible genetic basis for maxillary midline diastema and a greater role of environmental factors in the black sample than in the white sample.