Background: This paper presents psychometric properties of an instrument for the Assessment of Sexual Behaviour and Knowledge of people with Intellectual Disability (ASBKID), other-reported by professionals who are in daily contact with them. Methods and procedures: Assessments of 236 individuals with intellectual disability were obtained from 100 professionals. Results: Confirmatory factor analysis revealed a four-factor structure: concern about the user's inappropriate or uninhibited sexual behaviour; perception of the user's knowledge about privacy and social norms; perception of the user's knowledge about sexuality; and concerns about the user's sexuality. A multi-group CFA was also conducted in men and women, confirming the adequacy of this four-factor structure by gender. The reliability of the factors ranged from 0.74 to 0.92. Conclusions: The psychometric results obtained support the use of the ASBKID as a valid and reliable measure for the assessment of sexual behaviour and knowledge in both men and women with intellectual disability.