The new dad visited the Wolfson Surgical Suite where he saw sections of breast reconstruction surgery and a pioneering operation to remove a bladder tumour.
Upon arrival the hands-on royal, who had spent the morning supporting the Poppy Appeal at Kensington Palace with his wife Kate, donned his scrubs and got to work. When asked how he had fared, he held his tummy and replied, "Good. Still standing."
The 31-year-old then met members of the cancer hospital's surgical team involved in the operations, including the lead surgeons, Mr Stuart James and Mr Pardeep Kumar.
A hospital spokesman said, "Nobody fainted. The Duke was very calm, very interested in our pioneering, innovative surgery."
In May 2007 William was appointed president of the hospital, a position previously held by Princess Diana from 1989 until her death in 1997.
Although William and Harry's mother never watched surgery at the Royal Marsden, she did watch a heart operation at Harefield Hospital in Middlesex in 1996.
"He is president of the Royal Marsden so he needs to know about and get to see as much of the work that goes on there as possible," a Kensington Palace spokesman said ahead of his visit.
The Wolfson Surgical Suite was reopened in 2010 following extensive rebuilding and refurbishment after a fire destroyed the theatre area in 2008. He paid a visit to patients and staff affected by the blaze shortly afterwards.
The second in line to the throne was joined by his wife Kate to open the trust's cancer unit for children and young people at its hospital in Sutton, south London in 2011.