The nitric oxide (NO) field has been one of the most exciting scientific ventures over the past 10 years. Among the researches developed, the use of inhalation of NO gas allowed us to propose this therapy in lung diseases with promising results. Because of its property as a "selective" pulmonary vasodilator and because of its apparent clinical safety, inhaled NO has been proposed in acute lung injury (ALI) to improve severe hypoxemia. In this situation, the abnormal ventilation-perfusion ratio is improved by inhaled NO, limiting arterial hypoxia. The major clinical trials performed in adults, however, have failed to show any benefit on mortality and on mechanical ventilation requirements. Inhaled NO has been shown as an efficient therapy in pediatric ALI, probably because of a lower comorbidity. Because of the inhaled NO uptake by the lung, the extra vascular lung effects might be in the future the most important development in relation with platelet anti-agregant and anti-inflammatory properties.