Background: A positive conception of sexuality among people with intellectual disabilities is crucial and relies on several social and interpersonal contexts. The goal of this study is to analyse the interaction and impact of three different contextual groups: individuals with intellectual disabilities, their parents, and professionals working with them. Methods: Survey data were collected from 330 people with intellectual disabilities attending occupational centres in eastern Spain, 330 parents, and 100 professionals. Results: Correlation and variance analyses of dyad-level data show significant differences among the three groups in all variables. Professionals perceived people with intellectual disabilities to have higher knowledge of socio-sexual norms than people with intellectual disabilities actually appear to be, but they are also more concerned about aspects related to this area of people with intellectual disabilities. Compared to people with intellectual disabilities and professionals, parents perceived people with intellectual disabilities to have lower sexual knowledge. Conclusions: Our study demonstrates inconsistent perceived knowledge of people with intellectual disabilities' socio-sexual norms and sexual knowledge among the three groups, leading to disparate levels of concern regarding people with intellectual disabilities sexuality. Thus, the need to collect information from different perspectives for more accurate reporting and the critical need for sex education programs that involve the target population, but also parents and professionals who frequently interact with people with intellectual disabilities are highlighted.