OBJECTIVES: The Medication Compliance Questionnaire (MCQ) measures concepts that may be related to medication compliance by investigating subjects' motivation, barriers, attitudes, and beliefs regarding compliance. In the current study, the MCQ was administered in the Netherlands primarily via postal survey. However, due to low response rate to postal surveys in Italy, the MCQ was planned to be administered there primarily via telephone interviews. The primary goal of the study was to evaluate the equivalence of the postal mode of the MCQ against the telephone interview mode, to determine whether the results could be compared cross culturally. METHODS: Sixty subjects in Italy who responded to a postal administration of the MCQ were randomly assigned to one of two groups. Thirty subjects were administered the MCQ again approximately one week later by post and the remaining 30 subjects were administered the questionnaire again approximately one week later by telephone. RESULTS: As expected, results showed that the telephone mode of administration resulted in more complete data. Mail administration resulted in per item missing data rates of 3.3-23.3% while the phone administration yielded 100% response rates on all except one question, which was missing only one response. A difference in the consistency of responses across modes was found, with more consistency observed in the same mode between first and second administrations compared to alternate modes. There was also evidence of a response shift in the telephone administration mode including evidence for socially desirable response bias. CONCLUSIONS: Based on the results of this study, it is recommended that the results from the telephone administration not be considered equivalent to the mail administration without further examination. It is not advised to make direct comparisons of MCQ responses between countries without taking the potential impact of mode of administration into account.