A 17-year-old Japanese girl visited our hospital for an evaluation of exertional dyspnea. A diagnosis of pulmonary arterial hypertension (PAH) was confirmed based on the findings of right heart catheterization. Detailed questioning revealed a family history of hereditary hemorrhagic telangiectasia (HHT), and a genetic mutation analysis disclosed a mutation in the activin receptor-like kinase 1 gene (ACVRL1). The patient was finally diagnosed with HHT according to the Curaçao diagnostic criteria eight years after the diagnosis of PAH. This case supports previous reports indicating that signs of PAH can be the first manifestation of disease in ACVRL1 mutation carriers.