Facioscapulohumeral muscular dystrophy (FSHD) is an autosomal dominant neuromuscular disorder which maps to chromosome 4qter, distal to the D4S139 locus. The cosmid clone 13E, isolated in a search for homeobox genes, was subsequently mapped to 4q35, also distal to D4S139. A subclone, p13E–11, detects in normal individuals a polymorphic EcoRI fragment usually larger than 28 kilobases (kb). Surprisingly, using the same probe we detected de novo DNA rearrangements, characterized by shorter EcoRI fragments (14–28 kb), in 5 out of 6 new FSHD cases. In 10 Dutch families analysed, a specific shorter fragment between 14–28 kb co–segregates with FSHD. Both observations indicate that FSHD is caused by independent de novo DNA rearrangements in the EcoRI fragment detected by p13E–11.