Purpose Osteonecrosis of femoral head (ONFH) is a common joint disease with high morbidity in mainland China. We performed a retrospective case investigation based on the widest range of patients ever to reveal the demographic and clinical characteristics of ONFH in mainland China. Methods We collected data from hospitalized patients of nine large tertiary hospitals in China, focusing on the aetiology of ONFH. Medical records and self-design questionnaires were used to collect data. We determined the patients' aetiology according to established guidelines and categorized patients into different subgroups. We further analysed the underlying illness of the steroid-induced osteonecrosis of femoral head. Results A total of 6,395 patients with complete medical records were included in the study. The age (mean +/- SD) of the patients was 46.45 +/- 13.80 years. Males dominate with 70.1 % of all ONFH patients. In all the ONFH patients, 24.1 % are steroid induced, 30.7 % are alcoholic, 16.4 % are traumatic and 28.8 % are idiopathic. Among steroid-induced osteonecrosis of femoral head patients, 546 patients have autoimmune disorder (46.63 %), which is the most common underling illness, among these, the most common disease is systemic lupus erythematosus (SLE). Conclusions The most common age when ONFH occurs is between 40 and 50 years old. Male patients developed ONFH 3.4 years earlier than female patients. The number of the male patients is greater than the female, reaching the overall gender proportion of 7:3. Autoimmune disease is the primary cause of steroid-induced ONFH, among which SLE is the most common disease.