Objective: The aim of the study was to identify factors for treatment non-persistence in patients with ADHD. Method: Data for 100 patients with ADHD aged 5 to 16 who completed the Kiddie-Schedule for Affective Disorders and Schizophrenia–Present and Lifetime Version–Korean Version (K-SADS-PL-K) and Korean Wechsler Intelligence Scale for Children (K-WISC) were obtained between 2008 and 2013. Patients were classified as treatment-persistent and treatment-non-persistent based on 6-month follow-up. Sociodemographic data, comorbidities, intelligence quotient (IQ), severity, and social/school functioning were compared. Results: Adolescence and poor parental spousal relationships significantly predicted treatment non-persistence. Although comorbid major depressive disorder and absence of transient tic disorder were associated with treatment non-persistence, there was no difference in overall psychiatric comorbidity. No differences existed for IQ, Clinical Global Impressions–Severity (CGI-S) score, peer relationships, and academic achievement. Conclusion: Lower treatment persistence was associated with adolescence, comorbid depression, absence of tics, and poor parental spousal relationships, but not with symptom severity or impairment of the disorder.