GSM/UMTS base station as a unusual electromagnetic field source — Measuremenets in environment for LOS and NLOS scenarios In this paper authors describe the nature of electromagnetic field (EMF) in surrounding of a base stations (BS) – working in GSM900/GSM1800 and UMTS systems. Multi-frequency fields, pulse field and EMF variability in time are the main difficulties, which are emphasized in this study. Additionally, long term monitoring measurement from different locations in Wroclaw (Poland) are presented. Measurement has been carried out using EMF selective and broadband meters in urbanized area. EMF changeability trends were determined in measured period for GSM900/1800 and UMTS bands and two different locations for both, LOS and NLOS cases.