Efficient power control is of great importance in the design of high-capacity cellular radio systems. Optimum power control scheme (OPCS), in the sense that it minimizes the outage probability, has been fully investigated for frequency-division multiple-access/time-division multiple-access (FDMA/TDMA) cellular systems. In this paper, optimum power control theory is introduced to code-division multiple-access (CDMA) cellular systems to derive upper performance bounds for all types of transmitter power control schemes. Simulation results indicate that the OPCS will increase the CDMA system capacity by more than 1.9 dB over the perfect average power control scheme under IS-95-defined radio condition.