Although systemic lupus erythematosus (SLE) is a representative collagen disease, the etiology remains unclear. However, both genetic and environmental factors seem to be involved. Based on serological studies, associations between certain human leukocyte antigens and many autoimmune diseases have long been suggested. Regarding the genetic aspects of SLE, the HLA haplotype is regarded as a potentially important factor, although its role remains controversial. Recently, we examined three family members who had SLE with an identical HLA haplotype.