The aim of this study was to determine the environmental impact of organic dairy farms in the Austrian region of Flachgau. Effects of forage quality (low vs. high, i.e. 5.28 vs. 5.95 MJ NEL/kg dry matter, respectively) and performance level (from 5,000 to 8,000 kg of energy-corrected milk, ECM, per lactation) on greenhouse gas emissions as well as farm-gate balances of nitrogen, phosphorus and potassium were analysed using a farm model approach. Greenhouse gas emissions varied depending both on forage quality and level of milk yield. Regarding the greenhouse gas emissions per kg of ECM, per hectare farm land or per cow and year, lower emissions are achieved with high quality forage compared to low quality forage if performance levels are similar. This is mainly caused by the amount of concentrate feed imported in order to reach the desired level of performance as well as to provide balanced rations. When analysing parameters according to performance level, emissions per kg ECM decreased with increasing lactation milk yield. In contrast, emissions per hectare of totally utilised land area per year, per hectare of arable land per year and per cow per year increased with increasing lactation performance. To produce one ton of ECM, farms with high quality forage require considerably less arable land than farms with low forage quality. Use of arable land per ton ECM is lowest in farms with high quality forage and a lactation performance of 5,000 kg ECM. Considering balances of nitrogen, phosphorus and potassium, farms with low quality forage import higher amounts of nitrogen into the farm, particularly with increasing milk yield. In contrast, no considerable differences are detected between levels of performance and forage quality in phosphorus and potassium balances. The main sources for phosphorus and potassium imports are concentrate feeds and straw as litter for lying areas, respectively.