The aims of this study were to primarily investigate fatigue and sleep and to secondarily examine possible relationships between disease activity, pain, and functional ability in children and adolescents with juvenile idiopathic arthritis (JIA). Materials and methods: Ninety-six patients were enrolled in the study. Disease activity, functional ability, fatigue symptoms, fatigue severity, and sleep quality were assessed with the Juvenile Arthritis Disease Activity Score (JADAS), Childhood Health Assessment Questionnaire (CHAQ), Pediatric Quality of Life Inventory-Multidimensional Fatigue Scale (PedsQL-F), visual analog scale (VAS), and Pittsburgh Sleep Quality Index (PSQI), respectively. Results: Fatigue severity was moderate to high in 75% of patients with JIA and sleep quality was poor in 40% of them. VAS-fatigue was correlated with VAS-pain, VAS-wellbeing, PSQI, and sleep duration (P < 0.001). Significant relationships were found between the PedsQL-F and all other parameters except JADAS (P < 0.05). VAS-fatigue, CHAQ, and PSQI were identified as significant predictors of PedsQL-F (P < 0.05). Sleep quality, pain, and sleep duration were also significant predictors of fatigue severity (P < 0.05). Conclusion: This study suggests that fatigue and sleep problems are common problems in JIA. If underlying factors of fatigue and sleep are understood, strategies for improving sleep/fatigue paradox may develop in JIA.