This review focuses on the synthesis and use of the imidazolidin-4-one ring in synthetic and medicinal chemistry studies. It has remained remarkably under-utilized as a motif in drug discovery despite its obvious similarity to the widely encountered lactam pyrrolidinone, its isomer imidazolin-2-one and its oxidation state variants, the hydantoins (imidazolidendiones), imidazolidines, and imidazoles, as well as fused bicyclic ring systems. The synthesis of imidazolidin-4-one is reported in only 3 journal articles and a search for the explicit use of it in synthesis resulted in just 5 patents, and no academic journals. The specific sub-structure motif is reported in 296 journal articles and 65 patents. The different methods reported for creating substituted analogues will be discussed, as well as the application of the moiety in medicinal chemistry projects and alternative uses of these analogues as organic catalysts and prodrugs.