Arsenic, along with Hg, Sb, B, Li and F, is one of the important components of geothermal waters. In regions where geothermal waters are found abundantly, the arsenic content of these waters easily mixes into the watersheds and rivers. WHO reports the limit values of 10 mu g/1 for drinking waters, 19 mu g/1 for protection of aquatic life and FAO (Food and Agriculture Organisation) permissible limit for irrigation water (100 mu g/1). Arsenic, which is a natural pollutant in general, is of utmost importance due to its proven adverse impacts in particular on human health. Health problems due to high levels of arsenic are encountered in many countries such as Bangladesh, India, United States of America, Argentina, Chile, Taiwan and China. In this study, the arsenic content of the water and soil samples were evaluated to determine the impact of arsenic (As) pollution from geothermal sources on agricultural lands in Aydin-Germencik Alangullu Region which is a sub-basin of Great Menderes Basin (Western Turkey), where sodium chloride type geothermal sources are found as open systems. Water samples were taken from 4 different geothermal sources with natural flow conditions into agricultural lands of the basin. The As contents of the geothermal waters were measured between 680 and 1150 mu g/l. Soil samples taken from four different areas differed in relation to the impact level of the source and were determined to be between 14.88 and 48.50 mg kg-(1). The distribution of the impacted agricultural lands in the sub-basin was mapped using geostatistical methods.