Actress Charlize Theron was reportedly admitted to a Los Angeles hospital with an unknown and serious virus.

The Oscar-winning actress spent four nights at the Cedars-Sinai Medical Center last week after contracting a painful stomach virus, reported the National Enquirer.

The 'Monster' star reportedly suffered severe abdominal pains, which she attributed to food poisoning.

PHOTOS: Click for hot pics of Charlize Theron.

But when the sharp stomach pains failed to go away, Theron's boyfriend Stuart Townsend took the actress to Cedars-Sinai Medical Center to seek treatment.

Doctors ran a series of tests and diagnosed Theron with a serious virus thought to have been contracted during her travels overseas, according to the National Enquirer.

MORE: Go to News.co.au for more on Townshend's reaction.