Artemether-lumefantrine antimalarial efficacy in pregnancy could be compromised by reduced drug exposure. Population-based simulations suggested that therapeutic efficacy would be improved if the treatment duration was increased. We assessed the efficacy, tolerability and pharmacokinetics of an extended 5-day regimen of artemether-lumefantrine compared to the standard 3-day treatment in 48 pregnant women and 48 non-pregnant women with uncomplicated falciparum malaria in an open-label, randomized clinical trial. Babies were assessed at birth, 1, 3, 6 and 12 months. Nonlinear mixed-effects modelling was used to characterise the plasma concentration-time profiles of artemether and lumefantrine and their metabolites. Both regimens were highly efficacious (100% PCR-corrected cure rates) and well tolerated. Babies followed up to 1 year had normal development. Parasite clearance half-lives were longer in pregnant women (median [range]: 3.30 [1.39-7.83] hours) compared to non-pregnant women (2.43 [1.05-6.00] hours), p=0.005. Pregnant women had lower exposures to artemether and dihydroartemisinin compared to non-pregnant women, resulting in 1.2% decreased exposure for each additional week of gestational age. By term, these exposures were reduced by 48% compared to non-pregnant patients. The overall exposure to lumefantrine was improved with the extended regimen, with no significant differences in exposures to lumefantrine or desbutyl-lumefantrine between pregnant and non-pregnant women. The extended artemether-lumefantrine regimen was well tolerated and safe and increased the overall antimalarial drug exposure, and so could be a promising treatment option in pregnancy in areas with lower malaria transmission and/or emerging drug resistance (http://www.clinicalTrials.gov/;NCT01916954).