The number of online surveys in German official statistics has been steadily growing over the years as there is a huge demand in business, administrative statistics and in private households for responding by online questionnaires. Consequently, to guarantee a high quality of statistical data and to provide respondent-friendly online questionnaires, the Federal Statistical Office of Germany (Destatis) is testing electronic questionnaires. In doing so, a three step approach is applied: (a) observation while completing the questionnaire, (b) cognitive interviews (retrospective think aloud and probing) and (c) evaluation of eye tracking data. Based on tests of four different online questionnaire designs (CAWI instruments) and current research on the subject, the Federal Statistical Office developed preliminary guidelines for the design of online-questionnaires for private households. Final guidelines have not been released yet since further reflection is needed. In the focus of the paper are issues such as the general design of the questionnaire (paging or scrolling as a matter of navigation), visual design, kind and style of instructions, error messages, question and answering formats as well as the accessibility of the instrument. The paper highlights selected results from usability-tests with online-questionnaires and discusses how the design of online questionnaires can be enhanced.