Meiotic and mitotic chromosome numbers for Mentzelia leucophylla Brandegee (Loasaceae) are reported. The numbers of n = 11 and 2n=22 fit with the aneuploid series that exists in other taxa of Mentzelia section Bartonia, but differ from a chromosome number of n = 18 reported in 1973 by Reveal & Styer. Although additional work should be done on the species, it is suggested that the 1973 count may be in error.