The percentage of species having leaves with entire margins was determined at 38 sample sites in Costa Rica. The location of each sample site was plotted on Holdridge''s (1967) life zone chart, using the mean annual biotemperature, mean annual precipitation, and potential evapotranspiration ratio characteristic for that site. An attempt was made to correlate the percentage of species having leaves with entire margins with 1, 2 or all 3 of these climatic variables. No correlation could be found. The percentage of species having leaves with entire margins at a fossil locality was used by angiosperm paleobotanists to estimate paleoclimate. The lack of correlation found in Costa Rica suggests that a better correlation between leaf margin type and climate should be found before this characteristic is used to estimate paleoclimate.