Powder diffraction data are presented for 3,4-methylenedioxymethylamphetamine hydrochloride monohydrate, the hydrated form of MDMA.HCl, the drug of abuse commonly known as Ecstasy. Samples of pure MDMA.HCl were recrystallized from a variety of solvents, and powder diffraction patterns of the resulting products recorded. Data were collected at room temperature using iron-filtered CoKα radiation.