The first Medical Psychiatry Unit (MPU) in Japan was established in 1990. The clinical experience during the first 4 years of this unit is presented, and the characteristics of the Unit between its first 2 years and its latter 2 years are compared. The number of patients, the average length of stay, the primary psychiatric disorders, the combined physical diseases and their outcomes are presented. The data suggest that while the experience of the MPU is limited, it plays an important role in Japan as (i) an appropriate clinical setting for patients with combined medical and psychiatric illnesses, (ii) a strategic model for dealing with psychiatric patients in the general hospital, (iii) an educational setting for psychiatric residents to become more familiar with medicine and surgery, and (iv) an opportunity for non-psychiatric residents to become familiar with psychiatric illnesses and treatments.