Twenty-three of 25 Peruvian adults with chemodectomas of the head and neck had been born and lived at altitudes between 2105 and 4350 meters (6904 to 14,268 feet). Estimates of prevalence in Peru indicate that chemodectomas are about 10 times more frequent at high altitudes than at sea level. All carotid body tumors in the high altitude patients were benign; one other patient had a malignant glomus jugulare tumor. Females predominated over males in the proportion of 6.33:1 and left sided carotid body tumors over right sided in a ratio of 3.20:1. In only one instance was the carotid body tumor bilateral. One-half of the high altitude patients with carotid body tumors also had significant respiratory abnormalities. The present observations suggest that carotid body tumors in the high altitude native represent the extreme degree of hyperplastic response of chemoreceptor tissue to prolonged and severe hypoxia. © 1973.