Leaf mold, caused by the fungus Fulvia fulva, is an emerging disease in high tunnel tomato production in Illinois. Development of leaf mold on tomatoes in high tunnels was monitored during 2009-2010. Disease developed from mid to the end of the season. Symptoms of the disease occurred only on the foliage. Older leaves were first affected, with symptoms on younger leaves developed later. The first leaf symptom appeared as small, pale green lesions on the upper leaf surfaces, which gradually changed to yellow spots with indefinite margins. Fungal colonies developed on the corresponding areas of the lower leaf surface. The colonies appeared as dark olive green and velvety. Dense fungal colonies comprised of conidiophores and conidia. Conidiophores were unbranched, measured 120-185 μm long. Conidia were dark brown, with zero to three cross septa, and measured 14-42 × 5-8 μm. The withering and defoliation began in the lower leaves and progressed up the plants. Symptoms severity was higher in the tunnels with dense canopies. No symptom of leaf mold has been observed in any of more than 100 tomato fields and home gardens visited during 1999-2010 in Illinois. Thus, occurrence of leaf mold on tomato in Illinois appears to be limited to high tunnels production.