We report the cytogenetic findings in a rare tumor, a malignant fibrous histiocytoma of the gallbladder. Four related clones, two near-diploid and two near-tetraploid, which appeared to have been formed by a doubling of the near-diploid clones, were present. Numerous structural and numerical abnormalities characterized the tumor. Structural rearrangements included reciprocal translocations, translocations of unidentified material onto chromosomes, and deletions. Chromosomes involved in the rearrangements included 1, 3, 10, 12, 14, 16, and 19. Numerical changes included trisomy of chromosomes 2, 8, 10, and 20. Double minute chromatin bodies ranging in number from 5 to several were present in over a third of the cells.