In this work the corrosion behavior of an AlCrFeNiMn high entropy alloy is investigated to test its suitability for geothermal environments. The corrosion behavior in geothermal environments is unknown for high entropy alloys, the results obtained in this study add to the knowledge on this subject. The alloy was tested in-situ in geothermal steam at 200 degrees C and 1.65 MPa pressure at the Reykjanes Geothermal Power Plant in Iceland. The results revealed poor corrosion resistance of the AlCrFeNiMn alloy in the geothermal steam with high corrosion rates, an average of 3.25 mm/year. Microstructural analysis of the alloy revealed a corrosion layer depleted in aluminum, but rich in nickel, iron, and manganese sulfides and oxides, with MnS and Ni2S3 detected as the main constituents on the surface. The results of a surface tension test on the alloy showed a weak hydrophilic behavior of the surface that can increase transport of corrosive species to the underlying substrate and accelerate corrosion.