Therapeutic plasma concentrations of EFV (efavirenz) are between 1,000 ng/mL and 4,000 ng/mL. Concentrations below 1000 ng/mL are associated with higher risk of treatment failure, and concentrations above 4,000 ng/mL are associated with toxicity. The aim of the study was to appreciate EFV plasmas concentrations profile and the association between plasma levels and various characteristics in Beninese patients treated by a 600 mg standard daily-dose. Blood samples were collected and EFV plasma levels were measured by liquid chromatography coupled with mass spectrometry detection in HIV-infected patients receiving EFV in combination with other antiretroviral drugs for at least 14 days. Adverse effects occurring during treatment were collected through a questionnaire. An over-exposure to EFV among Beninese HIV patients were observed, with 46.4% of patients presenting EFV concentration above 4,000 ng/mL, although adverse effects were tolerated indicating that antiretroviral treatment is safe. The measurement of plasma concentration at the steady-state could contribute to early detection of treatment failure and adapt treatment in subjects presenting serious adverse effects within context of therapeutic drug monitoring.