Four patients with Proteus syndrome are reported; 3 of the 4 died of unusual causes. Current findings of the syndrome are reviewed, and the present state of its delineation is assessed with emphasis on what is known about natural history. Differential diagnosis includes neurofibromatosis, Klippel-Trénaunay-Weber syndrome, Maffucci syndrome, epidermal nevus syndrome, and the combination of Bannayan-Zonana syndrome, Riley-Smith syndrome, and Ruvalcaba-Myhre syndrome, now thought to constitute a single disorder. Conditions that may possibly overlap with Proteus syndrome--encephalocraniocutaneous lipomatosis and Thanos syndrome--receive special attention. Various suggested diagnoses for the elephant man's disorder are evaluated, and it is concluded that he suffered from Proteus syndrome, not neurofibromatosis. Finally, the psychosocial significance of elephant fever (EF) is discussed, and a plea is made for taking the EF out of NF.