The parabolic-trough collector (PTC) is the most commonly used technology in concentrating solar power (CSP) plants worldwide, and particularly in Spain. However, for now this type of large-size collector cannot be officially tested by an accredited laboratory or certified by an accredited certification body, as there is no standard adapted to it, and the current standards published for solar thermal collectors are not completely applicable. This paper summarizes the testing procedure and validation of a methodology for large size PTC collectors installed in solar thermal power plants. The testing methodology used was the one defined for conventional size solar collectors in quasi-dynamic state modified in the new revised version of international standard ISO 9806 which is referred to in the new standard IEC 62862-3-2 for CSP large-size PTC testing. The results of the optical and thermal efficiency of a large-size PTC are presented and compared to previous assessments of this collector. Hence, this paper validates the testing methodology for large-size PTC established in new standard IEC 62862-3-2, considering cleaning factor, polynomial heat loss model, incidence angle effects and quasi-dynamic conditions. (C) 2017 Elsevier Ltd. All rights reserved.