The purpose of this study was to investigate the efficacy of consultation-liaison (C-L) psychiatry from the perspective of medical economics, by comparing a part-time and full-time psychiatric department. One full-time (5 days per week) psychiatrist began work at a general hospital (GH-A), and one part-time (once per week) psychiatrist had been working at another general hospital (GH-B). Both general hospitals are teaching hospitals of the same size. The number of patients and the medical reimbursements were investigated each month and compared. This study demonstrated that the establishment of C-L psychiatry was economically profitable in contrast with what was the common belief among general hospital administrators. Also, the differences in the total number of patients (GH-A: GH-B = 500:35-50 patients/month) and the total reimbursement (GH-A: GH-B = 3 million: 2-300000 yen/month) was not explained by the number of working days (GH-A: GH-B = 5:1 day/week). The full-time model of C-L psychiatry has also indirect effects (i.e. educational and relieving effects) on the hospital staff. Promoting the establishment of C-L psychiatry requires many evidence-based studies that demonstrate the necessity for C-L psychiatry and can directly persuade hospital directors.