25 A systematic review of the literature INTRODUCTION The need for a specific evaluation instrument for motor abilities of children with severe multiple disabilities (SMD) has both nationally and internationally been recognised by physical therapists. Children with severe multiple disabilities (SMD) suffer from profound intellectual disabilities (IQ <25) and have a level of motor abilities comparable to level IV/V of the Gross Motor Function Classification System (GMFCS) for children with cerebral palsy (Palisano et al., 1997; Veugelers et al., 2005): they typically are wheelchair- bound and only a few are able to crawl or move with a physical aid (Mergler et al., 2012; Rieken et al., 2011). These children are most often severely limited in maintaining their body position or transferring into another position. In addition, children with SMD may have multiple sensory disorders and other co-morbidity such as swallowing and respiratory problems, epilepsy and contractures. As a result, children with SMD are fully dependent on their social and material environment for all activities of daily life. Motor abilities are essential for independent functioning, but are severely compromised in these children. Optimal development requires a highly structured environment with constant aid, supervision, extensive support technology and physical assistance (American Psychiatric Association, 2000). Independent mobility is only achieved if the child can learn how to operate a powered wheelchair (Palisano et al., 1997). Children with SMD often have to be manually activated and supported by caregivers to use their motor abilities. It has to be stressed that in the opinion of clinicians working in this field, even subtle motor abilities provide these children with a degree of control over their environment and may as such have influence on their quality of life. For the purpose of evaluation of interventions, measurement of motor abilities is essential. In current clinical practice, the evaluation of motor abilities by physical therapists is mostly based on subjective assessments in children with SMD or on instruments developed for other target groups. Nevertheless, standardised instruments developed for children with SMD with adequate psychometric properties are lacking. For this reason, an overview of psychometric properties is presented in this article of instruments that are not specifically developed for children with SMD, but for generic groups of children with severe disabilities.