Pulmonary hypertension (PH) at high altitudes presents unique characteristics due to hypobaric hypoxia. We aimed to evaluate the association between early diagnosis and clinical outcomes among children with severe PH living at high altitudes. A retrospective analysis was conducted on 86 children, divided into three age groups at the time of diagnosis: ≤3, 3-10, and ≥10 years. The median age at diagnosis was 4 years, with 48% of patients under 3 years old. Over a median follow-up of 6 years (interquartile ranges 2.5-8), 10% had a follow-up exceeding 15 years. Mortality rates were lowest in those diagnosed before age 3 (22% vs. 48% vs. 25%,