Background: Between 2004 and 2006, 1,170 Swedish soldiers were deployed to Liberia. They were prescribed mefloquine or atovaquone/proguanil as malaria chemoprophylaxis. Our study aims were to estimate the chemoprophylaxis effectiveness and adverse events.Methods: Cases of malaria were routinely reported during and after the mission. After return to Sweden, the soldiers filled in a questionnaire concerning type of accommodation, use of prophylaxis, and adverse events.Results: No cases of Plasmodium falciparum malaria were recorded during a total of approximately 7,000 person-months. Adverse events (AE) were reported by 57% in the mefloquine group and 34% in the atovaquone/proguanil group. In the mefloquine group, the soldiers reported more neuropsychological AE.Conclusions: Both drugs were safe and 100% effective as long-term prophylaxis for prevention of P. falciparum malaria. Atovaquone/ proguanil was better tolerated with respect to self-reported AE. [ABSTRACT FROM AUTHOR]