Introduction Systemic lupus erythematosus (SLE) is one of the most frequent autoimmune diseases. As SLE is unknown cause and difficult to treat, and the patients are forced to have difficult life, SLE is designated as one of the intractable diseases by Ministry of Health, Labour and Welfare of Japan, same as polymyositis and dermatomyositis (PM/DM) we report in another paper, the government provides those patients a financial aid for the treatment as a specific disease treatment research program. Simultaneously most of the patients are registered to a database, which includes basic information of patients' characteristics. Using this database, we can clarify in detail the characteristics of the SLE patients.

Methods In Japan, 21 405 SLE patients were registered in 2007. They are about 39% of the patients receiving financial aid by the government. We analysed the age, sex, age at onset, activity in daily life and clinical features.

Results In the registered patients, the number of male is 2336 and the female is 19 069, sex ratio is 0.12. Though an age distribution of male patients shows almost constant frequency from age 50s to 60s, that of female shows two peaks at age 30s and 50s. The age at onset of female SLE increases from teenage and shows one large peak at age 25–29. That of male does not show any significant peak.

Conclusion The characteristics observed here by the analysis of twenty thousand registered patients provided fundamental features of the disease.