The coiled-coil domain of dystrophia myotonica protein kinase (DMPK) has been cloned, overexpressed, purified and crystallized. Two crystal forms have been obtained that belong to space groups P3 and P2(1)2(1)2(1) and diffract to 2.4 and 1.6 A resolution, respectively. Experimental phases were obtained by MAD from an SeMet derivative. The location of selenium sites used molecular-replacement phases obtained from search models lacking sequence similarity with the coiled-coil under study. Both crystal forms contain three polypeptide chains in the asymmetric unit.