  We study from first principles the magnetism in graphene induced by single
carbon atom defects. For two types of defects considered in our study, the
hydrogen chemisorption defect and the vacancy defect, the itinerant magnetism
due to the defect-induced extended states has been observed. Calculated
magnetic moments are equal to 1 $\mu_B$ per hydrogen chemisorption defect and
1.12$-$1.53 $\mu_B$ per vacancy defect depending on the defect concentration.
The coupling between the magnetic moments is either ferromagnetic or
antiferromagnetic, depending on whether the defects correspond to the same or
to different hexagonal sublattices of the graphene lattice, respectively. The
relevance of itinerant magnetism in graphene to the high-$T_C$ magnetic
ordering is discussed.
