Expert guidelines recommend cognitive-behavior therapy (CBT) as a first-line treatment in pediatric obsessive-compulsive disorder (OCD) and the addition of selective serotonin reuptake inhibitors when CBT is not effective. However, the recommendations for CBT non-responders are not supported by empirical data. Our objective was to investigate the effectiveness of sertraline (SRT) versus continued CBT in children and adolescents that did not respond to an initial course of CBT. Randomized controlled trial conducted in five sites in Denmark, Sweden and Norway, 54 children and adolescents, age 7-17 years, with DSM-IV primary OCD were randomized to SRT or continued CBT for 16 weeks. These participants had been classified as non-responders to CBT following 14 weekly sessions. Primary outcomes were the CY-BOCS total score and clinical response (CY-BOCS <16). The study was a part of the Nordic Long-Term OCD Treatment Study (NordLOTS). Intent-to-treat sample included 50 participants, mean age 14.0 (SD = 2.7) and 48 (n = 24) males. Twenty-one of 28 participants (75%) completed continued CBT and 15 of 22 participants (69.2%) completed SRT. Planned pairwise comparison of the CY-BOCS total score did not reveal a significant difference between the treatments (p = .351), the response rate was 50.0% in the CBT group and 45.4% in the SRT group. The multivariate χ (2) test suggested that there were no statistically significant differences between groups (p = .727). Within-group effect sizes were large and significant across both treatments. These large within-group effect sizes suggest that continued treatment for CBT non-responders is beneficial. However, there was no significant between-group differences in SRT or continued CBT at post-treatment.