— In this paper we describe a knowledge-based approach that enables the subjective evaluation of portal and e-service quality by users in an adaptive manner. The model for adaptive quality measurement (MAQM) comprises different ontologies including concepts regarding quality aspects, questions and questionnaires, portal characteristics and problems encountered by users while using the portal. A prototype adaptive questionnaire system (SALT) which uses the MAQM model is also described. The system applies three axes of adaptation: based on real-time feedback from users through questionnaires, based on problems encountered by the user and based on metadata of the pages visited by the user. The results of evaluating SALT, compared to a static questionnaire, in an Austrian e-Government portal, are indicative of the value added of our approach. Adaptive systems; e-Government; ontology; quality measurement