Due to Colombia's geographical position, and taking into account the Colombian power utilities information, lightning is the main cause of disturbances and line outages on transmission and distribution circuits. This paper presents a study of lightning parameters using a software application named ZEUS developed using ArcView GIS 3.0a during 1996 and 1997 near power transmission lines of 230 and 500 kV of Interconexión Eléctrica S.A. (ISA), the main transporter of electrical energy in Colombia. The lightning information is supplied by ISA's detection network, consisting of six LPATS series IV sensors, which has operated since mid-1995 and covers the majority of the Colombian territory. In this work, an analysis of lightning parameters is carried out, identifying the country zones with high lightning current and ground flash density in order to determine the circuits with higher outage risk. The results contrast with analysis accomplished in other countries and contribute to the knowledge of lightning parameters in this tropical zone of the world.