Introduction The psychotropic medication and psychotherapeutic treatment of adults with intellectual disabilities study is a cross-sectional, epidemiological study carried out in Saxony, Germany. The main aim of the study is, among others, to assess the prevalence and quality of psychotropic medication in adults with ID. Methods Inclusion criteria are mild to profound forms of ID and an age of 18 years or older. A representative sample is realised by a two-stage sampling procedure. Study participants will be recruited from sheltered workshops (SW) and sheltered housings (SH). The stratified cluster sampling is realised by a random selection of service providing institutions followed by a random selection of adults with ID. An estimated total number of n=200 study participants via SW and n=400 via SH will be contacted to obtain data of approximately n=131 study participants recruited through SW and n=232 participants through SH. Thus, based on a psychotropic medication prevalence of 30%, an estimated number of n=109 in-depth interviews about psychotropic prescription practice will be carried out. Data collection is realised through interviews with key carers in the living environment. If psychotropics are prescribed currently, basic information (eg, dosage, treatment duration) are obtained, and a newly developed interview targeting the quality of the psychotropic medication treatment is conducted both with the carers and with the prescribing physicians. In addition to the prevalence and quality of psychotropic treatment, other parameters (eg, mental healthcare utilisation, psychiatric symptomatology, problem behaviour, institutional factors and parameters of the provision area) are assessed using well-established instruments. Ethics and dissemination Approval of the responsible ethics committee was obtained. Findings will be disseminated to participating institutions, published in journals and conferences and fill the lack of representative data that is urgently needed in this often criticised health service area. They shall help to improve mental health services in adults with ID prospectively.