Bell, 44, took over in April when Jim Cantalupo died suddenly of a suspected heart attack. Only a month later, Bell was diagnosed with colorectal cancer, a condition that has kept him from many of his duties. He had been with the company since he was 15.
Andrew McKenna, McDonald's chairman, said: "Charlie Bell has informed us of his decision to step down immediately from his role as president and chief executive officer of McDonald's to devote all of his time and energy to his courageous battle against cancer.
"On his behalf, he has asked me to thank everyone who is reaching out to him with thoughts and prayers."
McDonald's said that he would be replaced by Jim Skinner, currently vice-chairman, with Mike Roberts being promoted to president and chief operating officer.
Skinner, like Bell, is a McDonald's lifer, joining the company in 1971 as a restaurant manager trainee in Illinois. He has held positions at McDonald's all over the world, including a stint as president of McDonald's Europe from 1997 and 2001.
McKenna said: "In the course of his 33-year career at McDonald's, he has led every restaurant geography of the company and, like Charlie before him, his McDonald's roots are in the details and discipline of restaurant operations and customer service."
Roberts is promoted from his role of CEO of McDonald's USA, where he is credited with leading a resurgence of growth at the restaurant chain.
McDonald's most recent promotional work centres on the band Destiny's Child. The burger chain retains Leo Burnett for its advertising.
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