Background: Care and service trajectories for people with intellectual disabilities are routes within the health care delivery system that consist of all the steps that people with intellectual disability and their families have to take in order to realize needed care and services. In contrast to the growing body of system-orientated knowledge concerning quality of care delivered through collaborative relationships between care providers, specific user-orientated knowledge is still largely lacking. Aim: This article aims to describe the development and the preliminary validation of a user-orientated questionnaire for parents and/or relatives of people with intellectual disability (QUALITRA-ID-P) to assess the quality of care and service trajectories of their children/relatives with intellectual disability. Methods: First, the phenomenon "care and service trajectories" was conceptualized on the basis of document analysis and semi-structured interviews with key informants. Second, quality of care and service trajectories were operationalized using focus group discussions with parents and relatives as well as an extensive literature review. Third, the QUALITRA-ID-P was constructed using the results of the conceptualization and operationalization. Fourth, the QUALITRA-ID-P was refined in two stages: examination of (i) feasibility, understandability and completeness and (ii) preliminary validation. Results: The final QUALITRA-ID-P is a 49-item scale with good reliability and validity. An exploratory factor analysis resulted in a 3-factor solution with Cronbach's alpha coefficients of 0.98, 0.83 and 0.91. Organizations in the disability sector can use the QUALITRA-ID-P to understand better the experiences of quality of their clients' relatives and as a result improve the quality of trajectories.