A recent study has suggested that the A218G polymorphism in the homeobox A1 (HOXA1) gene may influence susceptibility to autism. We have determined the frequencies of the A and G alleles of the HOXA1 A218G polymorphism in both white and black patients from the South Carolina Autism Project (SCAP) and controls. Marked differences were found in allele frequencies between the races, but no deviations from Hardy-Weinberg equilibrium were seen in either white or black SCAP family members. More direct tests, comparing genotype frequencies between probands and controls and tracking transmission of the A versus G alleles to affected offspring, did not support the contention that allele status for the HOXA1 A218G polymorphism influences one's susceptibility to autism.