After upper limb deafferentation, adult macaques exhibit substantial reorganization of cortical somatosensory topography with enlargement of cortical areas responsive to facial stimuli. In the present study non-invasive magnetic source imaging technology has been used to map in detail the bilateral somatosensory homunculi in four neurologically normal controls and two upper arm amputees. Bilateral homuncular maps of normals and of the unaffected hemisphere of both amputees showed a wide hand area. The affected hemisphere of both amputees showed marked intrusion of facial representations into the digit and hand area consistent with the earlier observations in macaques. Our findings provide the first evidence of massive somatosensory plasticity in human adults and suggest a mechanism for post-amputation perceptual changes.