The paper investigates the quality of power supply to the Corporate Headquarters of the Power Holding Company of Nigeria (PHCN), PLC, Maitama, Abuja. This was facilitated by the measurements conducted using the harmonitor 3000 power analyzer on the secondary terminals of the two (2) 1000kVA, 11kV three-phase transformers serving the Company. The data on the network consisting of voltages, currents, power factor and harmonic distortion were acquired by the Harmonitor. Analysis of these data shows that there is significantly high variation between the minimum and the maximum voltage and that the phase loads are unbalanced. There is low power factor and the total harmonic distortions (THD) on the phases and neutral are high. The causes of the poor quality of power supply were identified and recommendations proposed taking into cognizance the complexity and sensitivity of the equipment in the network.