The provision of outpatient medical and contractual medical services by a GmbH has long been a contentious issue. Due to the intertwining of medical professional and contractual medical law, the topic initially required an intensive examination of the variably regulated medical professional law across different states. After determining the legal consequences arising from this, the contractual medical participation and cooperation system was discussed, including the GMG regulations for medical care centers (MVZ) and the corresponding legislative competencies. The author concludes that the contractual medical law as amended by the GMG only marginally opposes the doctors' or healing arts GmbH. The restrictions are primarily due to state legislative regulations of medical professional law, and only to the extent that the GmbH is not recognized as an MVZ. Ultimately, their unconstitutionality is established, indicating that the restrictions on the GmbH should be considered outdated.