Pediatric HIV-1 infections are still being diagnosed in France, despite the efficacy of prophylactic treatment to prevent mother-to-child transmission. To describe the characteristics and mode of infection of these children, we retrospectively analysed data of 59 children diagnosed with the HIV-1 infection between January 2000 and June 2005 in a Parisian university hospital. Twenty of these children had been born in France, and none had received appropriate prophylaxis (insufficient, not taken or given too late). Six received no preventive treatment due to failures in screening: three mothers were HIV-seronegative at the start of pregnancy and no test was carried out for the other three. At diagnosis, four had a severe immune deficiency (CD4 cells <15%). The 39 children born abroad were diagnosed at a median age of 3 years (range: 3 months-16 years), sometimes several years after their arrival in France. The clinical, virological and immunological status of these children was poorer than that of the children born in France: 18 had less than 15% CD4 cells. In contrast, the response to treatment of the children born in France was not as good as that of the children born abroad. The HIV-1 screening and prevention programme for pregnant women could be improved. Some children infected following the failure of prevention are at high risk of subsequent treatment failure. HIV-1 infection should be taken into consideration in children born in countries with a high prevalence of HIV, even if they have been living in France for several years and present no symptoms.