Background: People with intellectual disabilities are at increased risk of presenting behaviours that challenge. Behaviour support plans (BSPs) guide the use of bespoke strategies to maximise life quality and reduce the risk of behaviours that challenge. The behaviour support plan content appraisal tool (BSP-CAT) was developed to assess and improve the quality of BSPs. The aim of this study was to examine the reliability of the BSP-CAT. Method: Test--retest and inter-rater reliability were examined with the assistance of practitioners that supported adults with intellectual disabilities and behaviour that challenges. All participants received prior training and independently used the measure to score BSPs available to them. Results: Participants provided 98 BSP-CAT scores for 47 behaviour support plans. Good to moderate reliability was established at the total and strand level. Conclusions: Preliminary analysis suggests the BSP-CAT has encouraging reliability.