Millions of people worldwide engage in leisure or occupational activities in extreme environments. These environments entail health risks even for normal subjects. The presence of lung disease, or other conditions, further predisposes to illness or injury. Patients who have lung conditions should, but often do not, consult with their pulmonary clinicians before traveling. Normal subjects, including elderly or deconditioned adults, may be referred to pulmonologists for evaluation of risk prior to exposure. Other patients may present for consultations after complications occur. Pulmonary function testing before or after exposure can assist physicians counseling patients about the likelihood of complications.