OBJECTIVE: To understand the characteristics of HIV/AIDS patients with late diagnosis and find the factors associated with late HIV detection. METHODS: HIV late diagnosed patients and early diagnosed patients, which were identified and classified by definition in advance, were selected from the case reporting database of HIV/AIDS Comprehensive Response Information Management System in eight counties of four provinces (Zhumadian, Nanyang, and Zhoukou of Hennan province; Liuzhou and Lingshan county of Guangxi autonomous region; Guangzhou and Shenzhen of Guangdong province; Dehong of Yunnan province) between January 1, 2009 and June 30, 2010. A total of 3912 eligible patients were investigated, including 2496 late diagnosis and 1416 early diagnosis. The structured questionnaires were used to obtain information on behaviors, HIV detection history and reason of late detection for all eligible HIV/AIDS patients. Late diagnosed patients were defined by CD4 T-cell counts less than 200 cells/mm(3) or diagnosis as AIDS within the reported year after the first HIV positive test. The univariate and multivariate logistic regression methods were used to analyze the characteristics of HIV/AIDS late diagnosed patients. RESULTS: Only 14.2% (350/2469) of them have ever had the awareness of "to go for HIV testing", 68.8% (150/218)of which did not put it into practice within one month because of discrimination and stigma. Among those HIV late diagnosed patients without the awareness of "to go for HIV testing", the proportions of "never worried about HIV infection" or "never heard of AIDS" were 69.7% (1476/2116) and 18.1% (383/2116), respectively. When those HIV late diagnosed patients visited health settings because of AIDS related symptoms, only 40.0% (590/1475) of them received the HIV testing service. Furthermore, 54.5% (322/590) of those received HIV testing were not informed the results. Compared with early diagnosed patients, patients with late diagnosis were over 50 years old (OR = 4.14, 95%CI: 3.09 - 5.55), primary school education (OR = 1.29, 95%CI: 1.10 - 1.52) and illiteracy (OR = 2.15, 95%CI: 1.25 - 2.82), Routes of transmission from former illegal blood or plasma (OR = 2.91, 95%CI: 2.27 - 3.74) and transfusion of blood/blood products (OR = 2.79, 95%CI: 2.11 - 3.68). Late diagnosed patients were identified mainly from voluntary counseling and testing (45.4%, 1130/1528) and medical institutions (38.3%, 954/1469). CONCLUSION: The main reasons for late diagnosis of HIV infection are low initiative of HIV testing and discrimination and stigma. Furthermore, the low awareness of medical institutions to actively provide HIV testing affects the early diagnosis of HIV infections.