The purpose of this study was to develop a "Family Function Questionnaire for Families with Developmentally Delayed Children". The questionnaire was created by sampling 300 parents with developmentally delayed children. Initially, families and early intervention services were observed and a qualitative interview with the child's family was conducted. The researchers created a family function database reflecting these steps and by referral to relevant literature. The final version of the questionnaire consisted of 42 items in 11 categories: cohesion, education, problem solving, affective involvement, independence, action participation, family support, recreation, rules implementation, collaboration, and financial management. The questionnaire had a Cronbach's alpha of 0.9326.