The use of questionnaires in the study of occupationally acquired lung diseases was discussed. Questionnaires provided easily applied, inexpensive, and readily interpretable tools for the exploration of occupational health problems and associated risk factors. The use of established questionnaires, which have been verified for validity and repeatability was recommended when applicable. If drawing up a new questionnaire was necessary, the use of a limited number of closed ended questions to elicit the desired information was recommended. The importance of wording of questions was emphasized. The British Medical Research Council Questionnaire on Respiratory Symptoms (BMRC), was described as an example of an established medical questionnaire. Verification of the validity and reproducibility of a questionnaire were discussed. Interviewer differences were identified as the most common source of error in questionnaire studies. Other common source of bias included: differences in methods of administration of questionnaires, changes in questionnaire format, and seasonal effects. The problem of interviewer differences was eliminated with the self administered questionnaire, but these generated the problem of nonresponse and incomplete questionnaires especially with postal questionnaires. However, careful planning and execution of studies was shown to eliminate the problem of nonresponse. The author concludes that reliable and valid data may be obtained through questionnaire studies provided the correct techniques and procedures are followed.