Background: Individuals with an intellectual disability (ID) continue to experience major obstacles towards social, educational and vocational integration. Negative attitudes toward persons with ID has remained relevant over time and has led to discrimination and stigma. Objective: The present study describes the development of a new questionnaire for tapping into the general population's attitudes toward individuals with ID and addresses its psychometric properties. Methods: Adopting a multidimensional perspective, the "Attitudes Toward Intellectual Disability Questionnaire" (ATTID) was developed from a series of previously validated instruments and principles from the "Montreal Declaration on Intellectual Disability" (2004). The ATTID was administered by phone to 1605 randomly selected adult men and women, stratified by region in the Province of Quebec, Canada. Results: The ATTID yielded a five-factor structure overlapping the tri-partite model of attitudes. The cognitive component was represented by two factors: knowledge of capacity and rights and knowledge of causes of ID. The affective component tapped into two factors: discomfort and sensitivity/compassion. Finally, the behavioural component emerged as a single factor. The ATTID had good internal consistency with Cronbach's alpha coefficients ranging from 0.59 to 0.89 for the five factors and of 0.92 for the overall questionnaire. Test-retest reliability yielded correlations from 0.62 to 0.83 for the five factors. Conclusion: The ATTID can be used to measure attitudes among different populations and allows comparisons over time within the same population as a function of various intervention strategies for de-stigmatising ID. (Contains 3 tables.)