Among 165 HIV-infected patients, prevalence of SEN virus (SENV) infection was 51.5%, with subtype A predominance and unique SENV variant (67%), but also SENV superinfections with multiple variants were frequent. High prevalence, superinfection and broad SENV subtype diversification have been demonstrated, all linked to intravenous drug use (IVDU) as a risk factor for HIV acquisition. At multivariate analysis, SENV infection did not appear to have any negative impact on survival, while a possible protective effect needs further investigation.