Objective.—Our objective was to determine the incidence of acute mountain sickness (AMS) and the cardiorespiratory responses, in children and their parents, after rapid ascent to 3500 m. The sample population was composed of children and their parents who ascended within 24 hours from Arica (sea level) to Putre (3500 m) in Chile.

Methods.—Acute mountain sickness symptoms were evaluated using the Children's Lake Louise Score (CLLS) in children and the Lake Louise Scoring System in their parents. Heart rate, pulse oximetry, and AMS symptoms were evaluated in Arica before ascent, in Putre, and on return to Arica.

Results.—The mean CLLS was 10.8 ± 3 at Putre, with 92% of children developing AMS. Low oxygen saturation (80% ± 2%) and tachycardia (129 ± 9 beats/min) were observed in children with higher AMS scores. In contrast, parents had higher oxygen saturation (89% ± 3%), less tachycardia (87 ± 13 beats/min), and a 25% incidence of AMS.

Conclusions.—Our results indicate that children exposed acutely to high altitude are more sensitive to hypobaric hypoxia than are their parents, as manifested by symptoms of AMS, significant oxyhemoglobin desaturation, and tachycardia. Young children may experience an exaggerated hypoxemic response to high altitude exposure, and young age may be an additional risk factor for the development of AMS.