Little attention has previously been paid to the use of controlled vocabularies and subject keywords for indexing archival finding aids in the UK. Qualitative and quantitative responses to a questionnaire of UK repositories concerning the use of subject keywords and controlled vocabularies are presented. Clear patterns of thesaurus usage emerge from responses, and diverse opinions are put forward. Issues raised include retrieval by free text versus controlled vocabulary, strengths and weaknesses of different thesauri, lack of suitable thesauri, use of multiple thesauri, retrospective conversion, consistency of indexing across repositories and consistency of indexing across networks. Possible ways forward for the subject indexing of finding aids are identified.