Abstract
Lung agenesis is a rare condition which prognosis widely depends on associated malformations. Clinical presentation is so variable and diagnosis is often made in childhood. Here, we present a case of a 20-year-old girl who was admitted because of a spontaneous pneumothorax. Explorations concluded at a left lung agenesis, a hyperinflated right lung crossing the midline with a corresponding pneumothorax. There was no malformation else. This congenital condition and treatment for this rare presentation are discussed in detail.