Background Direct support workers (DSWs) accompany adults with autism spectrum disorder (ASD) and intellectual disability (ID) in residential care homes. Such DSWs, without specialised ASD training, are exposed to chronic stress linked to supporting ASD-ID clients and must adjust by coping strategies adapted to the needs of the residents. Nevertheless, difficulties adjusting constitute a burnout risk for DSWs, characterised by high levels of emotional exhaustion, depersonalisation and loss of a sense of personal accomplishment. We aimed to describe the burnout of DSWs who support adults with ASD-ID and to identify personal variables (experience and specialised training for ASD) and transactional variables (perceived stress and coping strategies) that could predict and mediate burnout. Method In total, 125 DSWs accompanying ASD-ID adults on a daily basis were included. Each participant answered four questionnaires measuring burnout, sociodemographic and professional variables, coping strategies and perceived stress. Results Five per cent of DSWs were in a state of burnout. Eighteen, six and fifty-nine per cent showed high average scores of emotional exhaustion, depersonalisation and loss of a sense of personal accomplishment, respectively. Being older, specialised training in ASD, stress perceived as a challenge and problem-focused coping strategies were associated with low levels of depersonalisation and loss of a sense of personal accomplishment. Conclusions Understanding the burnout process of ASD-ID DSWs may require the assessment of the organisational characteristics linked to the quality of life of the DSWs and the recognition of their specific needs when facing difficulties. The necessary ASD-focused training and support depends on an appraisal that would be individualised to adult ASD-ID DSWs.