•Analysis of the Theme zone in a learner corpus of English-medium Master's theses.•Czech students tend to use primarily simple unmarked two-component Theme patterns.•Overuse of textual and underuse of interpersonal Themes show rhetorical immaturity.•Textual Themes are realised mostly by conjunctive adjuncts and fewer conjunctions.•Interpersonal Themes are realised mainly by persuasion and obviousness markers. Drawing on Halliday's approach to information structure in discourse, this paper explores the discursive function of the initial part of the sentence, i.e. the Theme zone, in a learner corpus of Master's theses by Czech university students of English. The aims of the study are to identify the major patterns of Themes, to analyse the realisations of textual and interpersonal Themes and to compare the Theme choices in Czech students’ theses with the academic discourse of Anglophone student writers as illustrated by BAWE, and to consider how the findings of the study can contribute to the teaching of academic writing at university level. The results of the investigation show that Czech students tend to use primarily simple and two-component Theme patterns; textual Themes tend to be overused, whereas interpersonal Themes are strongly underused. Since the underuse or overuse of some thematic patterns and their realisations may be addressed by explicit instruction aiming at expanding the range of rhetorical resources that the students have at their disposal to build a coherent discourse, the findings of this study are intended to inform the design of courses and study materials for the teaching of academic writing at university level.