Objective: To investigate the tolerability of mefloquine intermittent preventive treatment (MQ IPTp) for malaria in HIV-infected pregnant women compared with HIV-negative women. Design: Prospective cohort study comparing samples of HIV-negative and HIV- infected pregnant women from 2 clinical trials conducted in Benin. Methods: One hundred and three HIV-infected women from the ongoing PACOME trial were compared with 421 HIV-negative women from a former trial, both trials aiming to evaluate the efficacy and tolerability of MQ IPTp, administered at the dose of 15 mg/kg. Descriptive analysis compared the proportion of women reporting at least 1 adverse reaction, according to HIV status. Multilevel logistic regression identified factors associated with the probability of reporting an adverse reaction for each MQ intake. Results: Dizziness and vomiting were the most frequent adverse reactions. Adverse reactions were less frequent in HIV-infected women (65% versus 78%, P = 0.009). In multilevel analysis, HIV infection [odds ratio (OR) = 0.23, 95% confidence interval (CI) = 0.08 to 0.61] decreased the risk for adverse reactions, whereas detectable viral load (OR = 2.46, 95% CI = 1.07 to 5.66), first intake (versus further intakes, OR = 5.26, 95% CI = 3.70 to 7.14), older age (OR = 1.62, 95% CI = 1.13 to 2.32), and higher education level (OR = 1.71, 95% CI = 1.12 to 2.61) increased the risk. Moderate and severe adverse reactions were more frequent when antiretrovirals were started concomitantly with a MQ intake. Conclusions: This study provides reassuring data on the use of MQ IPTp in HIV-infected pregnant women. However frequent, adverse reactions remained moderate and did not impair adherence to MQ IPTp. In this high-risk group, MQ might be an acceptable alternative in case sulfadoxine-pyrimethamine loses its efficacy for intermittent preventive treatment.