Background: Flooding in the greater New Orleans (GNO) area after the hurricanes caused extensive mold growth in homes resulting in public health concerns. Objectives: We conducted an environmental assessment of homes to determine the extent and type of microbial growth. Methods: We randomly selected 112 homes, stratified by water damage, and then visually assessed mold growth. Air samples from a subset of 20 homes were analyzed for culturable fungi, fungal spores, and markers of mold ((1-->3, 1-->6)-ß-d-glucans) and bacteria (endotoxin). Results: Visible mold growth occurred in 49 (44%) homes; 18 (16%) homes had greater than 50% mold coverage. Flood levels were greater than 6 ft at 20 (19%), 3-6 ft at 20 (19%), and less than 3 ft at 28 (26%) homes out of 107; no flooding at 39 (36%) homes. The residents spent an average of 18 h (range: 1-84) doing heavy cleaning and of those, 22 (38%) reported using an N-95 or other respirator. Visible mold growth was significantly associated with flood height greater than or equal to 3 ft and the predominant fungi indoors were Aspergillus and Penicillium species, which were in higher concentrations in homes with a flood level at greater or equal to 3 ft. Geometric mean (GM) levels of endotoxin were as high as 40.2 EU/m3, while GM glucan levels were as high as 3.5 µg/m3 even when flooding was less than or equal to 3 ft. Conclusions: Based on our observations of visible mold, we estimated that elevated mold growth was present in 194,000 (44%) homes in the GNO area and 70,000 (16%) homes had heavy mold growth. Concentrations of endotoxin and glucans exceeded those previously associated with health effects. With such high levels of microbial growth following flooding, potentially harmful inhalation exposures can be present for persons entering or cleaning affected homes. Persons exposed to water-damaged homes should follow the CDC recommendations developed following the 2005 hurricanes for appropriate respiratory precautions.