Background Persistent tachypnea of infancy (PTI) is a rare pediatric lung disease of unknown origin. The diagnosis can be made by clinical presentation and chest high resolution computed tomography after exclusion of other causes. Clinical courses beyond infancy have rarely been assessed. Methods Patients included in the Kids Lung Register diagnosed with PTI as infants and now older than 5 years were identified. Initial presentation, extrapulmonary comorbidities, spirometry and clinical outcome were analyzed. Results Thirty-five children older than 5 years with PTI diagnosed as infants were analyzed. At the age of 5 years, 74% of the patients were reported as asymptomatic and did not develope new symptoms during the observational period at school-age (mean, 3.9 years; range, 0.3-6.3). At the age of about 10 years, none of the symptomatic children had abnormal oxygen saturation during sleep or exercise anymore. Lung function tests and breathing frequency were within normal values throughout the entire observational period. Conclusions PTI is a pulmonary disease that can lead to respiratory insufficiency in infancy. As at school age most of the previously chronically affected children became asymptomatic and did not develop new symptoms. We conclude that the overall clinical course is favorable.