Abstract Background Juvenile idiopathic arthritis (JIA) is the most common rheumatic disease in the paediatric age. It is estimated that between 30–60% of adults patients persist with active disease, which leads to sequelae and complications as well as a decrease functional capacity and reduced quality of life. Objectives To evaluate the health-related quality of life in adult patients diagnosed with juvenile idiopathic arthritis. Methodology A cross-sectional study was performed, using a search for adult patients diagnosed with JIA between 1996 and 2018. Clinical records were reviewed during the paediatric age, and clinical parameters were evaluated for activity (JADASc-71), and joint (JADI-A) and extra-articular (JADI-E) damage, functional capacity (HAQ), and quality of life (SF-36). Relationships were determined by non-conditional logistic regression. Results A total of 69 patients were included. The most frequent subtype of JIA was enthesitis-related arthritis (ERA) (33%). Active disease was observed in 33%. Polyarticular JIA RF (+) was associated with active disease (P = .007), high values of JADASc-71 (P = .003), and HAQ (P = .001). Age of onset after 5 years reduced risk of joint damage (OR = 0.16) and extra-articular damage (OR = 0.03). Poor therapeutic adherence was associated with joint damage (P = .00) and JADASc-71 (P = .004). A high score of JADI-E was associated with functional disability (OR = 5.75). Joint damage (P = .003) and extra-articular damage (P = .024), and functional disability (OR = 7.05) were associated with low values in the SF-36. Conclusions JIA is not a disease limited to the paediatric age. Persistence of active disease, joint, and extra-articular damage are associated with functional disability and a decrease in H-RQoL.