There are many stories about John Aasen explaining his enormous height. For example, he was reportedly 20 pounds when born, his mother and grandfather were very tall (over 7 feet) and that the 8-foot giant Swede Nils Jansson Bokke may have fathered him. The probable truth is that his height was not genetic. His condition most likely was a form of “gigantism” caused by the over-secretion of growth hormone in the pituitary gland (termed "somatotrope adenoma"). This can be caused by a non-malignant tumor on the hypothalamus or pituitary gland

Unfortunately, as true with all those with this condition, John was gradually stricken with serious medical and emotional problems that forced him in and out of the hospital with increasing frequency during the last decade or so of his life. On the 1st of August 1938, at only 48 years of age, John Aasen died at the Mendocino State Hospital in California.

The ultimate height that John reached is still unclear. Various figures for his final height range between 213 cm (7’) and 274 cm (9’). The confusion is in part due to the fact that he continued to grow taller and taller, up to the year of his death, and in part because there was an unwritten law in the circus world that giants should never allow themselves to be measured. Every circus could then maintain that they had the world’s tallest man and no one could prove otherwise. Circus performers also used shoe insteps and other tricks to create the illusion that they were taller than they actually were.

That John Aasen ever achieved a height of 9 feet (274 cm) is nevertheless regarded as unlikely. However, copies of newspaper articles exist that indicated his height was well over 8 feet (244+ cm) at the time of his last hospital stay just before he died.

In spite of these divergent height estimates, the final answer appears to be within reach. It turns out that Johan Aasen was not buried in an ordinary manner, but rather his body was placed in a sealed container shortly after his death and sent by train to a Dr. Charles Humberd in Barnard, Missouri. Dr. Humberd was a highly educated scholar and renowned researcher on gigantism (and acromegaly) and was very well known for his work in these fields. Accordingly, John had visited Dr. Humberd on several occasions and had willed his body to Dr. Humberd after his death for research purposes and dissection. Charles Humberd must have been, let’s say, “a bit” eccentric. He had the skeletons of Johan Aasen and several other giants hanging from his living room ceiling up to his death in 1960. At this time, however, all traces of John’s remains, and the rest of Dr. Humbred’s morbid collection for that matter, disappeared for several decades. However two giant skeletons, one reportedly that of John Aasen, were recently found in an embryological museum in Loma Linda, California. If his identity can be made with certainty, something that should be possible with today’s DNA technology, a fairly precise measure of John Aasen’s height can finally be established.