Objectives: Up to 60% of women remove their levonorgestrel-releasing Intrauterine System (LNG-IUS) prematurely, mostly because of irregular bleeding disturbances up to six months after insertion. Assuming ongoing bleeding is due to atrophic bleeding of the endometrium, treatment with ooestrogen could be effective. No study in literature supports ooestrogen therapy for irregular bleeding in LNG-IUS users. Study design: A prospective cohort study was conducted in two hospitals to evaluate the effect of oral ooestradiol (started six months after LNG-IUS insertion) on irregular bleeding days. The participating women received 2mg ooestradiol daily for six weeks. We observed the discontinuation rate, the occurrence of adverse events and side effects due to ooestradiol. Women completed questionnaires at baseline and three months after start of the treatment. Results: Nineteen women were included. A median of 21 irregular bleeding days per month at baseline decreased to a median of five irregular bleeding days per month (p=0.003) after the use of ooestradiol for six weeks. Three out of nineteen women had their LNG-IUS removed at three months follow-up because of persistent irregular bleeding. No adverse events were reported, however, 68% of the participants reported side effects. Conclusion: In this study we observed a decrease in the number of irregular bleeding days in LNG-IUS users with ongoing irregular bleeding (>6 months after insertion), after administering oral ooestradiol for six weeks. We propose to conduct a larger prospective trial to evaluate ooestradiol as treatment option for irregular bleeding.