The paper presents a low-cost system for monitoring the condition of metal-oxide surge arresters (MOSAs) in service. The developed system integrates two methods currently used for evaluating the condition of surge arresters: registration of transient overvoltages experienced by a MOSA and analysis of leakage current. The system includes a set of sensors, a surge counters equipped with leakage current sensors (SCLCS), and one measuring unit. The SCLCS measures the current pulse charge, performs threshold selection of pulses, and registers the date and time. The registration data is stored in non-volatile memory. A measurement module connected successively to each SCLCS reads the registered data and also performs a comprehensive analysis of the MOSA leakage current: it identifies the resistive component of the total current; determines the phase angle between the voltage applied to the surge arrester and the first harmonic of the leakage current; performs a harmonic analysis of the leakage current. The voltage of one of the phases of a substation potential transformer is used as a reference signal, which is received via the radio channel from the transmitting unit of the system. The developed system for monitoring the condition of metal-oxide surge arresters was installed at several distribution substations. Long-term pilot operation of the system has shown that a comprehensive analysis of the leakage current allows not only to identify the deterioration of the technical condition of the MOSA, but also to determine the causes of degradation of the characteristics of the protective device. Data obtained by a SCLCS provides useful information on lightning and switching transient overvoltages arising in a particular network segment, the efficiency of the arrester operation, and the amount of energy absorbed by the MOSA. The paper describes the hardware implementation, operational principles, and main technical specifications of the proposed system. The results of the pilot testing of the system are presented.