Efficacious intervention for severe, treatment-refractory self-injurious behavior and aggression (SIB/AGG) in children and adolescents with intellectual disability and concomitant psychiatric disorders remains a complex and urgent issue. The aim of this study is to assess the efficacy of electroconvulsive therapy (ECT) on severe and treatment-resistant SIB/AGG in young people with intellectual disability and current psychiatric disorder. We reviewed the charts of all patients (N = 4) who received ECT in the context of SIB/AGG with resistance to behavioral interventions, milieu therapy and pharmacotherapy from 2007 to 2011. We scored the daily rate of SIB/AGG per patient for each hospital day. Inter rater reliability was good (intraclass correlations = 0.91). We used a mixed generalized linear model to assess whether the following explanatory variables (time, ECT) influenced the course of SIB/AGG over time, the dependant variable. The sample included two girls and two boys. The mean age at admission was 13.8 years old [range 12-14]. The patients had on average 19 ECT sessions [range 16-26] and one patient received maintenance ECT. There was no effect of time before and after ECT start. ECT was associated with a significant decrease in SIB/AGG scores (p < 0.001): mean aggression score post-ECT was half the pre-ECT value. ECT appears beneficial in severe, treatment-resistant SHBA in adolescents with intellectual disability.