Dementia with Lewy bodies (DLB) is commonly associated with excessive daytime somnolence (EDS). Modafinil is a wakefulness-promoting agent that is considered to have limited interaction with the dopaminergic system. As individuals with DLB are predisposed to psychotic symptoms which might be exacerbated by dopaminergic stimulation, modafinil is considered to be an attractive option for the treatment of EDS in DLB. We describe two cases in which administration of modafinil exacerbated agitation and hallucinations in DLB, and we also review data that may explain the mechanisms underlying this effect. In both cases, psychotic symptoms emerged concomitantly with modafinil administration, and remitted following its discontinuation. Although definitive data regarding the benefits and adverse effects of modafinil for the treatment of EDS in DLB await controlled prospective randomized studies, our observations warrant caution regarding its use in this context.