Recent trends in literature, along with the changes to the Diagnostic and Statistical Manual (DSM), make it imperative to study Attention-Deficit/Hyperactivity Disorder (ADHD) and Autism Spectrum Disorder (ASD) together, in order to better understand potential aetiological commonalities between these highly comorbid disorders. The present study examines social cueing, a highly studied construct in ASD, and intra-subject variability (ISV), a potential endophenotype of ADHD, in four groups of typically developing (TD), ADHD, ASD- (ASD without ADHD), ASD+ (ASD with ADHD) participants (N = 85) aged 10-13 years. Results showed that social cueing is intact in the 'pure' ASD group when task expectations are clear. The ADHD group showed faster saccadic reaction times, no increased ISV and a pattern of viewing comparable to the TD group. However, the ASD + group showed a differences in processing style and ISV. A secondary analysis gives evidence of non-additive effects of the ASD and ADHD factors.