A PID controller is designed by dominant poles placement method for an unstable first order plus time delay system. The robustness of the proposed controller is evaluated for perturbations in time delay, time constant and gain. The performance of the proposed controller is compared with that of the PID controller settings given by DePaor and O＇Malley (1989). The robustness of the control system is theoretically also evaluated by Kharitonov＇s method (1978).