In care substitution services, medical specialists offer brief consultations to provide general practitioners (GPs) with advice on diagnosis, treatment, or hospital referral. When GPs serve as gatekeepers to secondary care, these regional services could reduce pressures on healthcare systems. The aim is to determine the impact of implementing a care substitution service for dermatology, orthopaedics, and cardiology on the hospital referral rate, health care costs, and patient satisfaction. A before-after study was used to evaluate hospital referral rates and health care costs during a follow-up period of 1 year. The study population comprised patients with eligible International Classification of Primary Care codes for referral to the care substitution service (only dermatology, orthopaedic, cardiology indications), as pre-defined by GPs and medical specialists. We compared referral rates before and after implementation by χ2 tests and evaluated patient preference by qualitative analysis. In total, 4,930 patients were included, 2,408 before and 2,522 after implementation. The care substitution service decreased hospital referrals during the follow-up period from 15 to 11%. The referral rate decreased most for dermatology (from 15 to 9%), resulting in a cost reduction of €10.59 per patient, while the other two specialisms experienced smaller reductions in referral rates. Patients reported being satisfied, mainly because of the null cost, improved organisation, improved care, and positive experience of the consultation. The care substitution service showed promise for specialisms that require fewer hospital facilities, as exemplified by dermatology.