Errors, omissions, false understanding, and contradictory answers can compromise the use of questionnaires to generate follow-up data. To assess the utility of and effort involved in adding routinely a telephone interview to clarify the questionnaire, a study of total hip arthroplasty patients was carried out. Thirty-six patients with 37 primary and 13 revision total hip arthroplasties filled out a standardized questionnaire (which asks a number of demographic questions as well as questions that allow calculation of the Medical Outcome Studies [MOS] 36-Item Short-form Health Survey [SF-36], Western Ontario MacMaster Arthritis Center [WOMAC] osteoarthritis index, and Harris hip score) prior to returning for routine follow-up evaluation a minimum of 1 year after surgery. Two hundred thirty-two of a possible 4,350 responses (5.3%) were missing, contradictory, or answered with two or more answers on the questionnaire. Only eight such defects occurred following the telephone interview by a skilled orthopaedic surgeon, representing a significant reduction in these defects (P < .005). The average time of the telephone call was 2.8 minutes (range, 1-12 minutes), and the average number of attempts to contact the patient was 1.4 (range, 1-6). All questionnaire data and questionnaire data plus telephone data were compared with data obtained from a subsequent face-to-face interview by a different skilled orthopaedic surgeon who was blinded to the data from both the questionnaire and the telephone interview. It is demonstrated that a telephone call to follow up a standardized, self-administered questionnaire is a very effective way to augment the quality and quantity of questionnaire responses.