Anomalous muscles in the first flexor compartment of the forearm are quite common. Flexor digitorum superficialis (FDS) is a well known example (Kernohan et al. 1984; Ametewee et al. 1985; Elias et al. 1985; Tonkin & Lister, 1985). However, the anatomical variations of muscles, for example flexor digitorum profundus (FDP) in the second flexor compartment, are not rare (Hollinshead, 1969; Williams & Warwick, 1980; Honing et al. 1995; Williams et al. 1995). These muscles are usually asymptomatic and discovered incidentally during anatomical dissection or at operation. However, they may be symptomatic, presenting as an enlarging tumour-like mass simulating a ganglion (Vichare, 1970; Hayes, 1974; Murakami & Todani, 1982) or may cause a compression neuropathy (Hutton & Kernohan, 1981; Simodynes & Cochran, 1981).