The standard treatment for children with idiopathic pulmonary artery hypertension (IPAH) is epoprostenol. Few reports have evaluated oral bosentan therapy in children with severe IPAH. This report details the use of bosentan in a 16-month-old child with severe IPAH who presented as New York Heart Association (NYHA) functional class (FC) IV. His general condition, NYHA FC, serum aminotransferase levels, and arterial blood gases improved after 6 months of treatment. This case provides an example where twofold aminotransferase elevations suspected to result from right heart failure might not be a contraindication for bosentan therapy in children with IPAH.