Exposure to adverse natural and environmental events (eg, extreme temperatures and disasters) poses a public health burden when resulting in injuries requiring emergency care. We examined the incidence and characteristics of persons with environmental exposure-related injuries treated in US-based hospital emergency departments during 2001 to 2004 by using the National Electronic Injury Surveillance System-All Injury Program. An estimated 26 527 (95% CI = 18 664-34 390) injuries were treated annually-78% were heat-related. People with heat-related conditions were men (P < 0.001) and had a median age of 34 years (range = <1 month-94 years). Targeting vulnerable populations in community-wide response measures may reduce injuries from adverse environmental exposures, especially heat.