During the laboratory dissection of the fore arm, an accessory head of flexor pollicis longus muscle has been observed unilaterally in the right upper limb of a male cadaver. It took its origin from the under surface of flexor digitorum superficialis muscle just distal to the origin of this muscle from medial epicondyle. On further dissection we have noticed that, the accessory belly was running downwards to the medial aspect of the tendon of flexor pollicis longus muscle for its insertion. Its possible role in anterior interosseous syndrome is discussed in detail with a brief review