OBJECTIVES: To study whether linguistic analysis and changes in information leaflets can improve readability and understanding. DESIGN: Randomised, controlled study. Two information leaflets concerned with trials of drugs for conditions/diseases which are commonly known were modified, and the original was tested against the revised version. SETTING: Denmark. PARTICIPANTS: 235 persons in the relevant age groups. MAIN MEASURES: Readability and understanding of contents. RESULTS: Both readability and understanding of contents was improved: readability with regard to both information leaflets and understanding with regard to one of the leaflets. CONCLUSION: The results show that both readability and understanding can be improved by increased attention to the linguistic features of the information.