We assessed the effect of feeding damage by pear thrips, Taeniothrips inconsequens Uzel (Thysanoptera:Thripidae), on gas exchange and water relations of sugar maple (Acer saccharum Marsh.) seedlings. Compared to undamaged seedlings, feeding punctures in the leaf epidermis of thrips-damaged seedlings decreased water use efficiency, increased leaf conductance to water vapor, and decreased predawn water potential. Under conditions of high soil water and high light intensity, carbon dioxide exchange rate (CER) was greater for thrips-damaged than undamaged seedlings because of greater CO(2) conductance through feeding punctures. Under conditions of low soil water, CER was lower for thrips-damaged than undamaged seedlings as a result of water stress. Carbon dioxide exchange rate at low light and low soil water was limited by non-stomatal factors, but no difference in non-stomatal limitation to CER was detected between thrips-damaged and undamaged seedlings. Leaf tissue water relations differed between thrips-damaged and undamaged seedlings and under high and low soil water conditions. The results suggest that the reduction in leaf area of thrips-damaged seedlings can be partially compensated by elevated CER under conditions of high light intensity and high soil water. However, high gas exchange rates through feeding punctures predisposes thrips-damaged seedlings to water stress that can reduce CER under conditions of low soil water.