Background Owing to methodological issues, little research has been conducted to examine quality of life (QoL) as a treatment outcome in autism spectrum disorders (ASD) and intellectual disabilities (ID). This study was conducted to combine QoL measures and objective observations of challenging behaviours (CB) in order to evaluate changes over time in adults with ASD and ID who were treated in two different residential programmes; we hypothesised that a decrease in CB would be related to an improved QoL. Method In a longitudinal study (45 months), we followed 31 adults with ASD and ID who had been integrated into two residential programmes