The objective of this study was to assess the effectiveness of On Track Online, a psychosocial group intervention for adolescents with chronic illnesses (CI) that follows a protocoled online. In a parallel multicenter randomized controlled trial, adolescents (12–18 years) with various forms of cognitive impairment (N = 59; mean age = 15.1 years, SD = 1.7; 54% female) were compared with a waiting control group (N = 24) in On Track Online (N = 35). Online questionnaires were used for baseline (T0), 6-month (T1), and 12-month follow-up (T2) assessments. The main results were coping mechanisms connected to the condition and internalizing and externalizing behavioral issues. The quality of life related to health came second. To measure efficacy, linear mixed models were used. In terms of disease-related coping skills, T1 vs T0 (use of relaxation, β = 0.68; social competence, β = 0.57) and T2 vs T0 (information seeking, β = 0.61) showed a significant positive effect (p <.05) in comparison to the control group, as did HRQoL (social-, school-, psychosocial functioning and total HRQoL) T1 vs T0 (β = 0.52 to β = 0.60). There were no discernible intervention effects on behavioral issues that internalized or externalized. This randomized controlled trial's findings show that On Track Onlinehas a beneficial impact. The intervention improved HRQoL and coping strategies related to the disease.