Short-term cultures from three carcinomas of the gallbladder were cytogenetically analyzed. All three had an abnormal karyotype. The modal chromosome number was near- or hypertriploid in two tumors and near diploid in the third. Structural rearrangements of chromosomes 1 and 3, loss of material from the long arm of chromosome 18, and loss of chromosome 21 material were common to all three tumors and would seem to be the best candidates for nonrandom karyotypic changes in carcinomas of the gallbladder.