Sleep studies conducted at an altitude that is different from the home altitude can yield misleading results regarding the severity of obstructive sleep apnea (OSA). The objective of the present study was to determine the sleep characteristics of a patient undergoing polysomnography (PSG) in three Colombian cities at different altitudes (Bogotá, at 2,640 m above sea level [ASL]; Bucaramanga, at 959 m ASL; and Santa Marta, at 15 m ASL). The patient was an obese man with diabetes and suspected OSA. All PSG recordings were scored and interpreted in accordance with American Academy of Sleep Medicine criteria. In Bogotá, PSG revealed moderate OSA (an apnea-hypopnea index [AHI] of 21 events/h); in Bucaramanga, PSG revealed increased upper airway resistance (an AHI of 2 events/h); in Santa Marta, PSG revealed mild OSA (an AHI of 7 events/h). The reduction in the AHI was predominantly a reduction in hypopneas and obstructive apneas. The respiratory events were shorter in duration in the city at an intermediate altitude. Given that the AHI varied widely across cities, we can assume that the patient is normal or has moderate OSA depending on the city where he is. Central apneas were found to have no influence on the AHI.