The effect of previous physical conditioning on young well-conditioned mountaineers in relationship to acquiring acute mountain sickness is controversial. Data show both increased and decreased effects on the incidence of altitude illness. How general tourists at moderate altitudes are affected is unknown. To determine the influence of sea-level habitual physical activity on the incidence of mountain sickness, we surveyed 205 participants in a scientific conference at 3,000 m (9,840 ft). A 36-item questionnaire was distributed to the subjects 48 hours after arrival at altitude. Their sea-level physical activity (SLPA) was measured by a published and validated instrument that included questions about patterns of work, sporting, and leisure-time activities. Acute mountain sickness was defined as the presence of 3 or more of the following symptoms: headache, dyspnea, anorexia, fatigue, insomnia, dizziness, or vomiting. Most of the respondents were male (62%) from sea level (89%) with a mean age of 36 +/- 8.7 (standard deviation) years (range, 22 to 65). Nearly all (94%) were nonsmokers, and 28% had acute mountain sickness. The mean SLPA score was 8.0 +/- 1.3 (range, 5.1 to 12.0). No statistically significant difference in mean SLPA scores was found between those with and without acute mountain sickness (8.1 versus 7.8), nor in the individual indices (work, 2.5 versus 2.4; sport, 2.9 versus 2.7; leisure, 2.8 versus 2.7). We conclude that habitual physical activity performed at sea level does not play a role in the development of altitude illness at moderate altitude in a general tourist group.