A 12 year old female with three to four annual episodes of respiratory tract infections since age 2 months, was admitted to the hospital with the chief complaint of acute bronchitis. During her hospital stay, the diagnosis of left pulmonary hypoplasia was considered, which was lately confirmed by means of respiratory function tests, chest X-ray films, simple and perfusion gammagraphy as well as bronchography. During the 3 years follow-up, her body growth although below the third percentile for Mexican standards, has had normal annual increments (4.5-5.0 cm/year) and in the last eight months she has grown at a rate of 10.5 cm/year, simultaneously with the initial development of her secondary sexual characteristics. During the follow-up she has had only four minor episodes of respiratory tract infections which have been treated exclusively with symptomatic drugs. She is now under a program of pulmonary physiotherapy. It is concluded that throughout the years the right lung has satisfactorily compensated the initial deficit in pulmonary function and thus, is not only the degree of malformation, but also the complications secondary to it, with has a prognostic value for these patients, along with the supportive general medical management implanted.