The influence of pecan [Carya illinoinensis (Wangenh.) K. Koch] leaflet bronzing, a discoloration of the lower surface, on foliar physiology and nut-meat yield is unknown. Field investigations indicate that bronzing can adversely affect foliage by reducing net photoassimilation (A), stomatal conductance (sgw), and transpiration (E) while also altering stomatal aperture and cellular structure, and increasing temperature. Kernel weight and fill percentage are also reduced. Research indicated that foliar A declined in proportion to degree of bronze coloration, with negative A exhibited by heavily bronzed foliage. A by bronzed foliage did not increase as light levels exceeded ≈250 μmol·m-2·s-1. Within the same compound leaf, nonbronzed leaflets adjacent to bronzed leaflets exhibited greater than normal A. Bronzed leaflets also exhibited lower sgw to water vapor, less transpirational H2O loss, and higher afternoon leaf temperature. Light micrographs of bronzed foliage indicated abnormal epidermal and spongy mesophyll cells. Weight and percentage of kernel comprising the nut declined on shoots supporting foliage bronzing in July to August, but was unaffected when bronzing occurred in September to October. Bronzing of pecan foliage can therefore be of both physiological and economic significance.