Due to computer technology, a forced-response can be easily achieved in online questionnaires and is frequently used to gather complete datasets. An Internet-based quasi-experiment was conducted on the student server at the University of Vienna to study the influence of forced-response on dropout, demographic reports, and the content of the results. Forced-response was shown to substantially increase dropout. In addition, forced-response interacted with reported sex in eliminating a naturally occurring sex difference in dropout that was observed for the questionnaire whenever responses did not need to be enforced. Also reported sex turned out to have a mediating effect on time of dropout: Men dropped out earlier than did women. Further analyses revealed a reactance effect, as predicted by reactance theory. It is concluded that data from online questionnaires with forced-response designs are in danger of being hampered by dropout and reactance.