IntroductionThe elevated rates of neurodevelopmental disorders (NDDs) among siblings of children with autism spectrum disorder (ASD) raise concerns about their developmental monitoring and development. The main aim of this study is to assess the feasibility and acceptability of a standardised screening process on a large sample of siblings.Methods and analysisThis prospective study will assess the feasibility of a selective and multi-stage screening process for NDD performed on 384 siblings of children with confirmed ASD. Stage 1 will consist of the screening of NDD performed using online parental questionnaires (Social Responsiveness Scale, IdentiDys scale, DCDQ, parental concerns) through a web platform. In cases of a positive result, the second stage, consisting of a clinical semi-structured interview with a psychologist, will be proposed to the sibling before referral for diagnosis and treatment, if necessary. Approximately 12 months after stage 2, parents will be contacted by telephone to collect the diagnosis established following the referrals and their level of satisfaction concerning the screening process. Based on an expected participation rate of 50%, to estimate this rate with an accuracy of 5%, it is necessary to screen 384 subjects.Ethics and disseminationThe Ethics Committee on the Research of Human Subjects of Paris (Ile de France VII) approved this study in March 2022 (number: 2021-A02241-40). Express consent is required from all participants. Findings from the cohort study will be disseminated by publication of peer-reviewed manuscripts, presentations at scientific meetings and conferences with associated teams.Trial registration numberNCT05512637.