We aimed to identify risk factors associated with delayed diagnosis of HIV infection in a French region highly affected by AIDS. Data were collected in southeastern France through the HIV-surveillance system based upon anonymous declarations by laboratories and physicians prescribing HIV testing. From January 1996 to December 1997, 825 persons were diagnosed for the first time as HIV infected (female: 32%; >40 years: 28%); 46% had been infected through heterosexual intercourse, 26% through homosexual intercourse, and 19% through intravenous drug use. The semestrial (6 monthly) incidence rate decreased from 122.7 to 69.7 per million inhabitants (P<0.001). County of residence, age, sex, country of birth, and transmission category did not change significantly during the observation period. Twenty-seven per cent had a delayed diagnosis of HIV infection. This proportion did not differ significantly according to sex or country of birth, or during the observation period. However, after controlling for the other factors, delay was more frequent among injecting drug users (IDUs) (35%, P<10(-2)) than other transmission categories; it was also positively associated with age (47% above 50 years vs 13% under 30 years, P<10(-2)). This study highlights that, in spite of the current AIDS prevention policy and wide access to HIV screening, the proportion of delayed diagnosis of HIV infection remains high. Physicians should concern themselves with this public health issue, and campaigns should target people insufficiently aware, especially IDUs and older people. Further research is needed to understand better the causes of delayed diagnoses and of inequalities in access to HIV screening.