Robert reached a peak height of 2.72 m (8 ft 11.1 in), which is taller than an average grizzly bear standing on its hind legs. Robert’s extreme height was caused by hyperplasia of his pituitary gland, which produced an abnormally high level of human growth hormone.

When doctors examined Wadlow, they found that his extraordinary height was caused by hyperplasia of his pituitary gland. "The condition causes an abnormally high level of the human growth hormone and Robert was never given any treatment to stop it," Guinness World Records said.