BACKGROUND: Caring for a child with a disability can be especially difficult when the child exhibits challenging behaviours. Childhood disability often calls for the mother to be conscientious, capable and organized to meet the child's health and developmental needs. Mothers are known to feel particularly stressed when their child also behaves in ways that are difficult to manage. In these circumstances maternal mental health may be compromised and mothers therefore need more support. The Child's Challenging Behaviour Scale (CCBS) is an 11-item scale that measures a mother's report of challenging behaviours exhibited by their child with disability, that are associated with compromised maternal mental health and caregiving difficulties. This paper describes the initial development and psychometric evaluation of the CCBS. METHODS: A mixed methodology instrument design model was used to develop the CCBS. A qualitative study generated items, and quantitative data were collected from 152 mothers of a child with a disability. RESULTS: The CCBS showed excellent internal consistency (Cronbach's alpha = 0.89) and factor analysis supported its unidimensionality. Construct validity was supported by correlations with the PedsQL Psychosocial Health Summary Score (rho =-0.51) and cooperation taking medication (rho = 0.40). There were significant differences in CCBS scores between groups of children with and without either autism or psychiatric conditions. The CCBS showed moderate correlations with self-reported health status; the mother's sense of empowerment (rho =-0.44); and family cohesion (rho =-0.30). Mothers with a mental health condition recorded significantly higher CCBS scores. CONCLUSIONS: The CCBS is a brief, psychometrically sound instrument that provides clinicians with a new tool that measures a mother's rating of their child's behaviours that are challenging and associated with reduced maternal well-being. The CCBS assists professionals to identify mothers and family situations who may be in need of more support and interventions.