During the past 15 years, much has been learned about the human major histocompatibility complex. These new findings have been applied to the whole field of medicine, including transplantation immunology, blood transfusions, association with disease, human genetics, and the mechanism of human immune responses. In clinical medicine, the association between the major histocompatibility complex and various diseases has attracted the greatest interest. In this paper, we summarize the basic information on the human histocompatibility complex and its association with dermatologic disorders. Data from the world literature are reviewed and tabulated. Our own investigations on psoriasis, atopic dermatitis, and epidermolysis bullosa are discussed in detail.