Before launching a new study pilot testing is often recommended, however, it is seldom described in depth. Here, we report extensively on a pilot study using the internet as a new method for recruitment and data collection in a prospective cohort study of women planning a pregnancy.We aimed to enroll 2500 participants in six months and attained more than 75 % after 12 months follow up. To test data completeness and validity we randomized participants to fill either a long or a short version of the baseline questionnaire and compared self reported data with registry based data.We succeeded in enrolling 2288 participants, and participation rate was 82 % after 12 months. We found high correlations (0.96) for self-reported vs. registry based data and no difference in participation rate or data completeness according to questionnaire length. Overall, the internet based methods seem promising and we plan to launch the full study.