Methods: Design: Prospective, consecutive interventional study comparing a control group with standard counselling (phase 1) with an interventional group with counselling and application of the DA (phase 2). After completing phase 1 and 2 with a sample of 40 participants, we change the study design into a randomized controlled trial and randomize 88 participants in this part of the study. Sample: A total of 120 young cancer patients followed at one of the collaborating Swiss or German cancer centers aged 16 to 40 years who are possible candidates for FP . Intervention: Online DA, which is developed based on the applicants' research findings and on a prospectively evaluated fertility-related Australian decision aid booklet. Measures: Decisional Conflict Scale (DCS); items on knowledge, attitude and willingness concerning FP; decision regret scale (DRS); items on satisfaction and helpfulness of the DA.