Sixty-six cadaver hands were dissected to better define the anatomic variations of the first dorsal compartment and the superficial radial nerve. A septum was present in 31. A separate compartment enclosed the extensor pollicis brevis tendon in 29 and a slip of the abductor pollicis longus in 2. Multiple slips of the abductor pollicis longus tendon were noted in 38. Accessory slips inserted into the trapezium and thenar musculature. Partial separation or grooving of the abductor pollicis longus tendon was common but did not necessarily define a separate tendon slip.