Abstract Meiosis in American elm (a tetraploid with 2N = 56 chromosomes) was regular at all stages. Fifty well-spread cells at diakinesis or metaphase I from each of four trees showed that 28 bivalents were regularly formed. The average number of chiasmata per bivalent, determined from 18 cells, was 2.15 with a range of 1 to 4. The karyotype, as determined from observation of meiotic as well as mitotic cells, was found to be 52 telocentric or subtelocentric chromosomes and 4 submetacentric chromosomes. Relative chromosome lengths varied by a factor of 4 from largest to smallest, but no consistent size grouping could be determined. Mean short arm/long arm ratio for submetacentrics was 0.59 ± 0.03 (95% probability). Mitotic chromosome lengths were measured on a total of 13 metaphase plates from 9 genotypes. These observations indicate that this tetraploid should behave genetically as a diploid. Forest Sci. 21:123-127.