Abstract In an attempt to improve the knowledge of the quality of the thesauri-based databases (DB), a Spanish professional user group was surveyed in order to uncover DB thesaurus quality factors. Factor analysis methodology was applied to the data matrix gathered from users' opinions on a restricted sample of social science DB thesauri. Using processes of exploration, explanation, and interpretation, researchers reduced the initial 39 variables to 4 main components, regarded as the main DB thesaurus quality factors. These four main components are conceptual framework, performance, format, and external aids. They may provide scholars with four approaches to the issue of thesaurus quality and the points where further research is needed.