BackgroundHealthcare for people with somatic and comorbid mental diseases can pose a challenge to the healthcare system. The aim of the SoKo study (the Somatic care of patients with mental Comorbidity) is to assess the current state of care and the facilitators and barriers of somatic care of people with somatic disorders and comorbidity of a mental disorder.MethodsThe study is conducted as a mixed-methods approach and will include (a) descriptive and inferential analysis of secondary claims data of persons insured by a German statutory health insurance company in North Rhine-Westphalia (Techniker Krankenkasse, TK-NRW), (b) qualitative individual interviews and group discussions, and (c) based on (a) and (b), quantitative surveys of both patients and physicians. We intend to analyse a sample of claims data of about 2.6 million persons insured by TK-NRW (group comparisons between TK-NRW insured persons with a diagnosis of a prevalent somatic disease [ICD-10-GM E01–E07, E11, E66, I10–I15, I20–I25, I60–I64] with and without comorbidity of a mental disorder [F00–F99]), in order to assess the uptake of somatic care by people with mental and somatic comorbidity. In addition, primary data from patients with the aforementioned somatic illnesses and a mental comorbidity as well as primary data from physicians (general practitioners and medical specialists) will be collected. The focus here will be on support factors and barriers in the somatic care of people with mental comorbidity.DiscussionUp to now, there have been no published results of a systematic collection of both secondary and primary data on the utilisation of different care services of somatically ill patients with mental comorbidity for Germany. The present mixed-methods study aims to address this gap.Trial registrationThe trial is registered with the German Clinical Trials Register DRKS: DRKS00030513. The trial was registered on 3rd February 2023.