Particular risks and recommendations are identified for backpacking, trekking, scuba diving, snorkeling, spelunking, white water rafting, sailing, backcountry snow skiing, climbing, and mountaineering. Pre-travel screening for medically austere and physically demanding destinations should concentrate on underlying cardiovascular risk and occult medical and psychiatric conditions. When a malaria chemoprophylactic agent is needed, doxycycline may have an added benefit in this cohort because the extreme traveler may have more environmental exposures that place them at higher risk for zoonotic diseases. For example, exposures to fresh water or to grassy brush and wooded outdoor areas where ticks are common increase the risk for leptospirosis and rickettsial diseases, respectively.