Among the enhanced properties of the 1,3-dibromo-5,5-dimethylhydantoins described are their larger average particle sizes, their compactibility even though devoid of a binder, their excellent free-flowing and low-dust properties, and their more appealing aesthetic qualities, as compared to previously known 1,3-dibromo-5,5-dimethylhydantoins. These novel 1,3-dibromo-5,5-dimethyl-hydantoins can be produced, for example, by concurrently feeding (i) an aqueous solution or slurry formed from an inorganic base and 5,5-dimethylhydantoin, and (ii) a brominating agent, in proportions such that each nitrogen atom is substituted by a bromine atom, thereby forming product which precipitates in an aqueous reaction mixture. The pH of the reaction mixture is maintained in the range of 5.5 to 8.5.