Background: The increasing popularity of mountain climbing will result in greater numbers of the general population being at risk for the disturbances known to occur with altitude exposure. Methods: Observations of sleep and breathing were made in 6 healthy travellers (5 males and 1 female, 38 to 62 years of age) before, during, and after a recreational climb. We modified a portable seven channel polygraph to record sleep state, oxygen saturation, respiratory movements, body position, and oronasal airflow 4 weeks prior to the expedition at home (500m), at base camp (4200m) and in 3 climbers at 6400m. All had a repeat study at 500m altitude 4 weeks after the expedition. Results: For the group, the total number of obstructive apneas and hypopneas (OA/H) at night increased from 36 at home to 68 at base camp over a one night recording. Separately counted central apneas and hypopneas (CA/CS) increased from 6.7 to 45. In one climber, who had a history of recurrent snoring and observed apneas at home, the number of apneas increased from 201 at 4200m to 322 at 6400m, whereas in 2 climbers measured at 6400m, all apneas decreased. The total sleep time (TST) increased in all 6 climbers by 10% at base camp in comparison to home records. In the 3 climbers attaining an altitude of 6400m, the REM (rapid eye movement) sleep declined by 10% compared to the record at 4200m. Conclusion: Respiratory disturbances at low altitude are amplified by exposure to high and extreme altitude. In those without symptoms of sleep apnea, significant physiologic alterations will occur at high altitude but at extreme altitude regular ventilation is re-established.