The present study aimed to investigate the long-term quality of life (QoL) in a large sample of pediatric obsessive-compulsive disorder (OCD) patients. The study included 220 pediatric OCD patients from the Nordic Long-term OCD Treatment Study (NordLOTS) who were evaluated at seven time points before, during, and after stepped-care treatment over a 3-year follow-up period. Data from three symptom severity trajectory classes formed the basis of the QoL evaluation: acute (n = 127, N = 147), slow (n = 46, N = 63), and limited responders (n = 47, N = 59). Patients' QoL was assessed using parent and child ratings of the revised Questionnaire for Measuring Health-related Quality of Life in Children and Adolescents (KINDL-R). QoL was analyzed by trajectory class using a random mixed effects model. The association between pre-treatment factors and long-term QoL was investigated across classes in a multivariate model. Three years after treatment, the acute responder class had reached QoL levels from a general population, whereas the limited responder class had not. The slow responder class reached norm levels for the child-rated QoL only. Higher levels of co-occurring externalizing symptoms before treatment were associated with lower parent-rated QoL during follow-up, while adolescence and higher levels of co-occurring internalizing symptoms were associated with lower child-rated QoL during follow-up. For some patients, residual OCD symptoms in the years after treatment, even at levels below assumed clinical significance, are associated with compromised QoL. Co-occurring symptoms could be part of the explanation. Assessing QoL after OCD treatment, beyond the clinician-rated symptom severity, could detect patients in need of further treatment and/or assessment. Trial registry: Nordic Long-term Obsessive-Compulsive Disorder (OCD) Treatment Study; ; ISRCTN66385119.