To examine the degree of exact and partial match between the assigned descriptors and title keywords of medical theses written in Farsi and submitted for a PhD degree.Design/methodology/approach – A sample population of 506 theses in Pediatrics, Gynecology, Cardiology and Psychiatry was randomly picked out of a total of 909 indexed in the Indexing Department of the Central Library of the Iran University of Medical Science and Health Care Services. The results obtained are compared with those reported for other documents written in Farsi and English. Where applicable, the influence of the foreign language and its structure is commented on.Findings – It is shown that the degree of match between the assigned descriptors and the title keywords is greater than 70 per cent, equaling those reported for Farsi books and Michigan University Library catalogue in USA. It is also shown that the frequency of the match has increased since 1982, indicating that the authors have become more attentive in their choice of title.Research limitations/implications – Detailed analysis of results, however, shows significant differences between the degree of exact match amongst the four categories, with psychiatry theses that use more common terms showing highest exact match findings (50 per cent).Originality/value – This paper highlights the need for a closer collaboration with medical institutions for definition of approved terms and their incorporation in indexation in order to improve findings in various medical categories.