The importance of format, graphic layout, and ques- tion routing instructions on the quality of survey data has been acknowledged for self-administered survey instruments, but the significance of these factors for questionnaires administered by interviewers has not been recognized equally. This paper exam- ines two studies in which interviewers used different question- naire designs to administer the same set of survey questions to randomly selected adult respondents in housing units that made up area probability samples of the Detroit metropolitan area. The paper presents empirical evidence of specific effects (questions skipped in error, unprobed answers) directly attributable to the choice of questionnaire design. The analysis shows that question- naire design choices can either help or hurt the quality of data collected by interviewers. Furthermore, the behaviors of experi- enced and inexperienced interviewers are affected in similar ways. In other words, interviewing experience does not compen- sate for format deficits in the design of survey instruments. Questionnaire design is frequently overlooked as an important aspect of the development of field instruments and as a potential source of independent effects on survey estimates. Discussions about topics such as question formatting options, graphic layout, integration of in- terviewer recording tasks for complex question series, and optimal routing strategies are frequently absent from published works that oth- erwise deal with questionnaire development. The quality of questionnaire design is generally recognized as an important factor for self-administered instruments (Dillman 1978, 1983); however, the importance and special problems of design for questionnaires to be administered by interviewers has not been ac