Background: Youth with ASD are at risk to develop low self-esteem, which is related to both co-occurring internalizing- and externalizing problems. In this RCT (N=24) we aimed to test the efficacy of Competitive Memory Training (COMET) for low self-esteem in youth with ASD (8-16y). Method: We compared the combination of COMET and Care As Usual (COMET+CAU) with CAU-only, to explore whether COMET had additional effects on low self-esteem and co-occurring symptoms of youth with ASD. Stability of effects was measured seven weeks later. Results: Participants receiving COMET+CAU showed greater improvement on parent-reported self-esteem and externalizing symptoms than participants receiving CAU-only. Similar improvements between groups were found on self-reported self-esteem and depressive symptoms. Improvements remained stable until seven weeks after having received COMET+CAU, with depressive symptomatology improving even further. Conclusions: Given the small sample size and mixed results, this pilot study does not allow us to declare COMET as being necessary in enhancing low self-esteem in ASD. However, this study indicates that when given parallel to CAU, COMET can help to improve self-esteem and co-occurring externalizing problems in youth with ASD in only a short period of time.