The deep (motor) branch of the ulnar nerve is not frequently seen during surgery, but is vulnerable to penetrating injury and may be injured during surgery. Its anatomy is poorly described and its three-dimensional configuration is poorly appreciated.In this study, dissections of ten cadaveric specimens have been performed to demonstrate the branching pattern of the nerve and its skeletal relations have been clarified by superimposing images on radiographs. The deep branch passes downwards (anatomical posterior) through a hypothenar fibro-muscular tunnel and courses radially on the surface of the interossei. It has four major divisions that are consistent and readily identifiable. Twenty branches were documented supplying hypothenar muscles, medial two lumbricals, interossei, adductor pollicis, all the carpometacarpal and the ring and little metacarpophalangeal joints, and opponens pollicis in 40% and flexor pollicis brevis in 20% of subjects.