Achillea millefolium L. (yarrow) from Bulgaria was extracted in a supercritical pilot-scale plant using carbon dioxide (CO2). First, the extraction yield was studied as a function of time at 14 MPa, 40 degrees C and 70 g/min of CO2. Then, the extraction time was set in order to study the effect of different process parameters (pressure, temperature, CO2 flow and use of ethanol as co-solvent) on the extraction yield. The composition of the volatile oil obtained in yarrow extracts was thoroughly studied by GC-MS. Overall extraction yield increased with pressure, temperature and amount of co-solvent. Nevertheless, minor effect of the studied process parameters on yarrow volatile oil profile was found. On the other hand, important differences were found when comparing the volatile oil composition of BulgarianAchillea millefolium L. extracts with those obtained from other origins. (C) 2016 Elsevier B.V. All rights reserved.