ObjectiveTo compare the effectiveness of a hysteroscopic niche resection versus no treatment in women with postmenstrual spotting and a uterine caesarean scar defect.DesignMulticentre randomised controlled trial.SettingEleven hospitals collaborating in a consortium for women's health research in the Netherlands.PopulationWomen reporting postmenstrual spotting after a caesarean section who had a niche with a residual myometrium of ≥3 mm, measured during sonohysterography.MethodsWomen were randomly allocated to hysteroscopic niche resection or expectant management for 6 months.Main outcome measuresThe primary outcome was the number of days of postmenstrual spotting 6 months after randomisation. Secondary outcomes were spotting at the end of menstruation, intermenstrual spotting, dysuria, sonographic niche measurements, surgical parameters, quality of life, women's satisfaction, sexual function, and additional therapy. Outcomes were measured at 3 months and, except for niche measurements, also at 6 months after randomisation.ResultsWe randomised 52 women to hysteroscopic niche resection and 51 women to expectant management. The median number of days of postmenstrual spotting at baseline was 8 days in both groups. At 6 months after randomisation, the median number of days of postmenstrual spotting was 4 days (interquartile range, IQR 2–7 days) in the intervention group and 7 days (IQR 3–10 days) in the control group (P = 0.04); on a scale of 0–10, discomfort as a result of spotting had a median score of 2 (IQR 0–7) in the intervention group, compared with 7 (IQR 0–8) in the control group (P = 0.02).ConclusionsIn women with a niche with a residual myometrium of ≥3 mm, hysteroscopic niche resection reduced postmenstrual spotting and spotting‐related discomfort.Tweetable abstractA hysteroscopic niche resection is an effective treatment to reduce niche‐related spotting.