We present two patients with sickle cell trait (HbAS) who developed acute sickle cell crisis after passive exposure to high altitude on the Jungfraujoch (3454 meters, 11,333 ft). Both suffered splenic infarction and the first patient also presented with acute renal failure. Splenic infarction is known to be a complication of altitude exposure in carriers of the trait, whereas acute renal failure due to altitude exposure alone has as far as we know never been described in the literature. These forms of high altitude complications are totally unusual in Switzerland.