The endometrial effect of long-term vaginal oestriol (E3) therapy for urogenital atrophy was assessed in 23 post-menopausal women. Hysteroscopic and histological examinations were performed in each patient to assess endometrial atrophy before treatment and after 6 and 12 months of therapy (0.5 mg vaginal E3 for 21 days, then 0.5 mg twice weekly). The primary atrophic picture was confirmed at the end of the 6th month in all but one of the patients. In one case, the histology showed an abnormal stromal reaction with no epithelial alterations. Treatment was continued and after the 12th month complete atrophy was confirmed both hysteroscopically and histologically in all patients. Efficacy as regards vaginal and urogenital complaints was good. Our results demonstrate that in women with endometrial atrophy effective and well-tolerated treatment with vaginal E3 can be safely continued for up to 12 months.