Chronic mountain sickness (CMS) and high altitude pulmonary hypertension (HAPH) have been well described in different mountainous regions of the world as chronic high altitude (HA) diseases. This review briefly summarizes the available data from some genes known to be regulated by hypoxia-inducible factor 1 (HIF-1) and/or by hypoxia that have been studied in populations from these regions suffering from CMS and/or HAPH. Excessive erythrocytosis, caused by a lower oxygen saturation and hypoxic ventilatory response and/or ventilatory inefficiency, is the outstanding sign of CMS, and right ventricular enlargement, pulmonary hypertension, and remodeling of pulmonary arterioles are hallmarks of HAPH. Familial character and heritability studies have suggested that genetic factors could make a contribution to the pathogenesis of CMS and HAPH. Even though some alleles are more prevalent (G allele of eNOS polymorphism Glu298Asp in Sherpas and ACE I allele in HAPH Kyrgyz) or less prevalent (ACE D allele in HA Andeans) in the different high altitude populations, published data to date are insufficient for a rigorous test of any hypothesis regarding the implications of these gene polymorphims in CMS or HAPH. © 2008 Mary Ann Liebert, Inc.