The benefits and environmental risks of genetically modified (GM) spring wheat with improved powdery mildew resistance were investigated on two field sites by a consortium of Swiss research groups from 2008 to 2010. GM wheat lines with specific powdery mildew resistance and general fungal resistance were compared with control lines, commercial wheat varieties, and with barley and triticale. The impact on insects and soil organisms (bacteria, mycorrhizal fungi, soil fauna) as well as outcrossing to wheat were investigated in addition to powdery mildew resistance. Several GM wheat lines were significantly more resistant to powdery mildew than their controls. No relevant impact was found on non-target organisms, their biodiversity or selected ecosystem services. On the whole, the differences between GM and control lines were smaller than between commercial wheat varieties or other cereal crops. Outcrossing events were rare and found only at a short distance from GM test plants.