In this paper, we derive analytical expressions for outage probability and ergodic capacity of a spectrum sharing system with multiuser diversity under Nakagami-m fading. In particular, multiuser diversity effects in such systems where several secondary users utilize the licensed spectrum of the primary user are considered. The best and worst channel quality scenarios are investigated for transmission from a number of secondary transmitters. Numerical analysis and simulations are shown to reveal the effects of multiusers and fading parameters on the considered system.