Imidazolidinones and imidazolidine-2,4-diones are important classes of heterocyclic compounds that possess potent activities against several viruses such as dengue virus, enterovirus, hepatitis C virus (HCV), and human immunodeficiency virus (HIV). The first imidazolidinone derivative as an anti-HIV agent was reported in 1996. Imidazolidinones inhibit HIV aspartic protease activity, and also act as CCR5 co-receptor antagonists. Significant effort has been devoted to the design of various imidazolidinone analogues that are active against drug-resistant HIV strains, with fewer side effects. Different scaffolds have been designed through both rational drug design strategies and computer-aided drug design. Imidazolidinones have been found to be potent against HIV, and preclinical studies are currently in progress. There are some reports of imidazolidinones as having both anti-HCV and anti-dengue virus activity, and more research has yet to be done along these lines. These compounds inhibit NS3 serine protease of HCV, and NS2B-NS3 protease of dengue virus. Pyridyl-imidazolidinones possess very specific and potent activity against human enterovirus 71 (EV71) by targeting the EV71 capsid protein VP1, and inhibiting viral adsorption and/or viral RNA uncoating.