Incidence and malignant forms of imported Plasmodium falciparum malaria are increasing, and chemoprevention is more and more replaced by stand-by treatment and radical cure in preventing access on return from malaria areas. Halofantrine is recommended for this radical cure: it's an habitually well-tolerated amino-alcohol with very few side-effects. We report three cases of long QT-interval due to halofantine: three different young women coming back from Africa took halofantrine (500 mg (2 tablets) six hourly for three doses on the first and the seventh day) and all presented with syncopal episodes. Serum electrolyte concentrations and echocardiograms were normal. In one case only, a diagnosis of Plasmodium falciparum malaria was made, without severe manifestations, and in the two other cases, treatment was a radical cure. In two cases, several bursts of torsades de pointes ventricular tachycardia due to halofantrine were proven and electrophysiological cardiac tests concluded that they had a congenital long QT-interval/Romano-Ward syndrome). So far halofantrine cardiac toxicity was unknown with single dose of 24 mg/kg/d. This phenomenon can be very severe in case of preexisting cardiopathy. In spite of the rarity on the congenital Romano-Ward syndrome, systematic electrocardiogram is necessary before giving halofantrine.