The Environmental Symptoms Questionnaire (ESQ) was developed to provide a standardized procedure for assessment of symptoms experienced by soldiers exposed to environmental extremes. It was used initially to delineate the symptoms of acute mountain sickness, but it has since been expanded into a more comprehensive tool for measuring subjective reactions to severe heat and cold, as well as to diet, physical exercise, and medications. The ESQ has also been made more reliable and user friendly by revision, addition, and removal of certain items and by compression of the initial scale values. Factor analysis of responses obtained during exposure to environmental extremes has identified several meaningful symptom clusters and has provided the basis for developing a useful technique for scoring the questionnaire based on the item clusters. Studies utilizing the ESQ under various environmental extremes are summarized and reviewed. Current techniques for administration and methods for scoring are included.