The authors report five cases of apparently lone atrial fibrillation in five members of the same family from three generations. The atrial fibrillation occurred at an early age and rapidly became permanent in all cases. With time, in the absence of complications, structural cardiac abnormalities were documented by echocardiography (biatrial dilatation and mitral and tricuspid regurgitation). These observations raise the question of genetic predisposition to lone atrial fibrillation at least in this particular clinical context.