OBJECTIVES: To define the scoring and assess the psychometric properties of a newly developed questionnaire measuring the impact of child gastroenteritis on parents. METHODS: A literature review was conducted to create the first conceptual model. Semi-directive interviews of 10 parents were conducted and analysed to create items. A 54-item self-administered questionnaire was simultaneously developed in French and UK English and cognitive debriefings were conducted with 5 parents. The questionnaire was linguistically validated in Spanish, Italian and Polish and included in an observational and prospective study conducted with 302 parents of children under 5 presenting at the general practitioner/paediatrician site with acute gastroenteritis. Multitrait analysis and item content were used to confirm the dimensions and define the scoring of the questionnaire. Internal consistency reliability (Cronbach’s alpha), floor and ceiling effects, scale-scale correlations and criterion validity of the resulting version were assessed. RESULTS: The final version of the questionnaire consists of 44 items in five dimensions: “Symptom Severity” (13 items), “Parents’ Worries due to Symptoms” (8 items), “Child’s Behaviour” (6 items), “Impact on Parents’ Daily Activities” (10 items) and “Parents’ Distress” (7 items). Higher scores indicate higher levels of negative feelings. All the scores presented good psychometric properties: no dimension had a floor or ceiling effect, Cronbach’s alpha ranged from 0.78 to 0.85 showing a good internal consistency reliability, and scale-scale correlations ranged from 0.41 to 0.67 showing consistency but no redundancy between the dimensions. Correlations with Clark’s and Vesikari’s scores showed a good criterion validity. The more severe the gastroenteritis episode, the higher the scores of the questionnaire. CONCLUSIONS: The “Impact of child gastroenteritis on parents” questionnaire allows a very complete overview of how an episode of severe gastroenteritis impacts the parents of the ill child. The questionnaire is a valid and reliable instrument, suitable for future studies.