The aim of the present study was to investigate variations of the musculus flexor digitorum brevis. We examined 33 feet in total from 15 embalmed adult cadavers and three lower extremities. Of the 33 feet examined, 18 differed from the classical description given in anatomical textbooks. The muscle belly for the fifth toe was much smaller than the others in 12 feet and was missing in six feet. Two cases had extreme variations. In the left foot of one female cadaver, the flexor digitorum brevis was formed by a superficial and deep head, which had three muscle bellies and four tendons. In the right foot, a separated muscle belly for the fifth toe was very thin and originated from the intermuscular septum as a flat fascia under the flexor digitorum brevis. In another case (male), three heads (lateral, intermediate and medial) formed the quadratus plantae and the lateral and intermediate heads fused with the flexor digitorum brevis. Variation of the flexor digitorum brevis may be important clinically because of reconstruction of the heel pad by flexor digitorum brevis musculocutanous flap transfer. © 2005 Japanese Association of Anatomists.