Fluctuating asymmetry—small random deviations from perfect bilateral symmetry—is commonly used as an indicator of environmental stress. I used the extent of fluctuating asymmetry in leaves to evaluate the degree to which heavy metal contamination has an observable phenotypic effect on the developmental stability of Rhus glabra (Anacardiaceae), the smooth sumac. Sumac from a deserted mining site near Picher, Oklahoma, displayed significantly greater size-corrected unsigned fluctuating asymmetry than that of sumac from a control site near Tulsa, Oklahoma. These results suggest that heavy metal contamination has a significant effect on the stability of developmental processes in R. glabra and suggest that fluctuating asymmetry may be used as an indicator of environmental pollution.