Young has presided over the launch of eight treatments, including the HIV Truvada combo, while revenue has soared to $10B in 2012 from $1.24B in 2004.
The timing of Young's departure could be a bit awkward, as Gilead recently received approval to launch Sovaldi, a potential blockbuster treatment for Hepatitis C.
The Street's Adam Feuerstein notes that Young has sold $17M in stock since August, while the top five managers have offloaded almost $220M worth of shares, a sum that "is just too big to ignore."
Says a hedge a fund manager: "The bigger question is whether there's a motivation issue at Gilead. The top executives are all insanely rich."