This paper will present DRAMBORA (Digital Repository Audit Method Based on Risk Assessment), a methodology and tool for auditing a trustworthy digital repository of grey literature. DRAMBORA is an online instrument which helps organizations develop documentation and identify the risks of a digital repository. DRAMBORA is accessible from http://www.repositoryaudit.eu. The paper will also summarize prevailing advantages and disadvantages of DRAMBORA. The second part of this paper will describe the audit of the National Repository of Grey Literature (NRGL) as a trustworthy digital repository using DRAMBORA as part of creating a digital repository of grey literature in the National Technical Library (NTK). The most important outcome of the audit was represented by the identified risks connected to the repository and potentially endangering its operation, quality, image, and other features. The main principle of the DRAMBORA audit and, at the same time, its main contribution, is its iteration (i.e. its repetition after a certain time period in new conditions when the original risks are reassessed; the measurements adopted for solution are assessed and new risks are identified).