The article reports on a case study of impact evaluation of external quality assurance, i.e. programme accreditation, which was carried out by the Catalan University Quality Assurance Agency at Autonomous University of Barcelona in the form of a methodological before-after comparison. The impact evaluation exhibits a marked stability of the attitudes towards quality assurance of different stakeholders and shows that the majority of teachers do not perceive effects of quality assurance in learning and teaching. The analysis further indicates that teachers' awareness of certain quality assurance instruments increases during accreditation and that university leadership is seen as highly supportive for quality assurance by teachers. The study also demonstrates that for teachers the perceived amount of expenditure is clearly higher than the perceived benefit. Finally, a series of open answers gives indications for possible improvement of the university's quality assurance and organizational structures.