Mujica met Obama in the Oval Office for talks focusing on wider US-Uruguayan relations and issues including education, trade and economic issues.
But he made a point of bringing up Uruguay's tough restrictions on smoking, which have led to it being sued for $25 million by US tobacco giant Philip Morris at the World Bank's International Center for Settlement of Investment Disputes (ICSID).
Mujica told Obama, a reformed smoker, that eight million people a year were dying from tobacco-related illnesses, as the two leaders held a photo-op in the Oval Office.
"That is more than World War I, (and) World War II," he said.
"It's murder. We are in an arduous fight -- very arduous -- and we must fight against very strong interests," Mujica said through a translator.
"Governments must not be involved in private litigation, but here we're fighting for life.
"Nobody must be distracted in this fight for life, because out of all values, the most important one is life itself."
In March 2006, Uruguay became the first Latin American country and the fifth nation worldwide to implement a ban on smoking in enclosed public places.
It also enacted some of the world's toughest tobacco laws, requiring large health warnings on packages and banning advertising and the use of multiple products for one brand.
Philip Morris, owner of the Marlboro brand, is the largest cigarette manufacturer in the United States. It has huge global business interests and its case against Uruguay is being closely watched.
The company, which is headquartered in Lausanne, contends that the anti-smoking rules infringe Uruguay's investment treaties with Switzerland.