Regional trends of variation of heat flow in western Anatolia have been outlined using the silica temperature estimator on thermal springs. Silica heat-flow values from 187 springs have been calculated. The data are corrected for local long-term mean annual surface temperature. A mean value of heat flow for the western part of Anatolia of 107 ± 45 mW m - 2 has been obtained, which is about 60% above the world average.The silica heat-flow data are compared with available conventional heat-flow values for this region. A general agreement is observed, and new patterns are recognized. A close association exists between areas of high silica heat-flow values (above 100 mW m - 2 ), and areas of Tertiary and younger volcanism. High heat flow is also observed in Palaeozoic units of the Menderes Massif which is under tensional stress. The highest heat-flow estimate of 247 mW m - 2 is obtained near Gediz (38°57 N, 29°13.2 E). This area is part of a seismically active region and is located near a Middle Eocene subduction zone which is an area of later collision tectonics.The new heat-flow data from western Anatolia improve our knowledge of the thermal conditions within the crust. This information is important for the analysis of various geophysical and geological phenomena including seismicity.