The purpose of this study was to investigate how response rates to a postal questionnaire are affected by title and length of the survey instrument. Five questionnaires, which differed according to title and length, were designed. Each questionnaire was mailed to a random sample of one thousand Norwegian women aged, 35-49 years. A total of 3,106 questionnaires were returned (62.1%). The highest response rate (70.2%) was achieved by a two-page questionnaire entitled "Women and Cancer". An otherwise identical questionnaire entitled "Oral Contraceptives and Cancer" had a response rate of 60.7%. Questionnaires entitled "Women and Cancer" with a length of four and six pages had a response rate of 62.8% and 63.3%, respectively. The four page questionnaire entitled "Women, Lifestyle and Health" had the lowest response rate of 57.1%. This study shows that in a general population of Norwegian women the title of a postal questionnaire influences the response rate. The results indicate that although the shortest questionnaire had the highest response rate, the most extensive survey instrument did not have the lowest response rate. The distribution of risk factors for breast cancer did not vary according to response rate or design of questionnaire. The overall findings of this study suggest that the benefits from the increased information obtained from extensive postal questionnaires out-weighs a potential non-response bias due to a somewhat lower response rate.