Objectives: Children with juvenile idiopathic arthritis (JIA) may be predisposed to serious pneumonia due to modern disease-modifying anti-rheumatic treatment. In this nationwide retrospective study with clinical data, we describe the pneumonia episodes among children with JIA. Methods: Patients under 18 years of age with JIA and pneumonia during 1998–2014 were identified in the National Hospital Discharge Register in Finland. Each individual patient record was reviewed, and detailed data on patients with JIA and pneumonia were retrieved, recorded, and analyzed. If the patient was hospitalized or received intravenous antibiotics, the pneumonia was considered serious. Results: There were 157 episodes of pneumonia among 140 children with JIA; 111 episodes (71%) were serious (80% in 1998–2006 and 66% in 2007–2014). The mean age of the patients was 9 years. Forty-eight percent had active JIA and 46% had comorbidities. Disease-modifying anti-rheumatic drugs (DMARD) were used at the time of 135 episodes (86%): methotrexate (MTX) by 62% and biologic DMARDs (bDMARD) by 30%. There was no significant difference in the use of bDMARDs, MTX and glucocorticoids between the patient groups with serious and non-serious pneumonia episodes. During six of the episodes, intensive care was needed. Two patients (1.3%) died, the remaining ones recovered fully. Conclusions: Although the incidence of pneumonia and the use of immunosuppressive treatment among children with JIA increased from 1998 to 2014, the proportion of serious pneumonias in these patients decreased. There was no significant difference in the use of anti-rheumatic medication between patients with serious and non-serious pneumonia.Key Points• The incidence of serious pneumonias decreased from 1998 to 2014 among children with juvenile idiopathic arthritis (JIA).• There was no significant difference in the use of the disease-modifying anti-rheumatic medication between JIA patients with serious and non-serious pneumonias.• Active JIA, comorbidities, and combination medication were associated with nearly half of the pneumonias.