Markham Stouffville Hospital officials aren't saying how many people have the potentially deadly bacteria, but say two units at the Markham site are affected.
The hospital says it is limiting visits to patients on those units in an effort to prevent the spread of the infection.
Hospital workers are also ramping up handwashing and equipment cleaning procedures.
C. difficile is a bacterial infection that can lead to diarrhea in those who contract it.
There have been a number of outbreaks of the infection at hospitals in other areas of the province.