Since 2002, an undescribed fungal disease has become an important problem on creeping bentgrass in the Southeast. Symptoms of the disease initially appear as areas of wilt, drought stress, or chlorosis ranging in size from 6 to 60 cm in diameter. Examination of roots from affected plants reveals dead root tips, loose cortical structure, and an absence of root hairs. Additionally, abundant hyphae and oospores of Pythium spp. are frequently observed in the cortical tissues. These symptoms and signs are characteristic of Pythium root dysfunction as described by Hodges and Coleman in 1985. Isolations from multiple bentgrass samples in North Carolina and Virginia displaying symptoms of Pythium root dysfunction consistently yielded Pythium volutum and Pythium torulosum. Pathogencity of these species was determined by inoculating mature creeping bentgrass plants with 5 isolates of P. volutum, 2 isolates of P. torulosum, and a combination of the two species. There were 10 replications of each treatment. Inoculated plants were incubated for four weeks at 26C/15C to permit root infection, followed by a heat stress period at 34C/26C to induce foliar symptoms.  Typical foliar symptoms developed two weeks after raising the temperature to 34C/26C. All isolates of P. volutum were highly aggressive on creeping bentgrass roots (70 to 100% disease) compared to isolates of P. torulosum, which caused only 10 to 20 % disease.  Isolates of P. volutum also consistently decreased root mass and root depth compared to P. torulosum and the uninoculated control. Pythium volutum was readily reisolated from diseased tissue and re-inoculations were retested to confirm pathogencity.  Our data indicate that P. volutum is the most important causal agent of Pythium root dysfunction in North Carolina.