Objectives The strong association between atypical endometrial hyperplasia and endometrial carcinoma is well established, but data on the risk of atypical hyperplasia and carcinoma in Danish women with non-atypical endometrial hyperplasia are almost non-existent. This study aimed to investigate the prevalence of atypical hyperplasia and endometrial carcinoma diagnosed within 3 months of initial diagnosis (defined as concurrent disease) and the risk of atypical hyperplasia and carcinoma more than 3 months after initial diagnosis (classified as progressive disease) in Danish women initially diagnosed with non-atypical endometrial hyperplasia. Design This cohort study recruited 102 women diagnosed with non-atypical endometrial hyperplasia at Randers Regional Hospital in Randers, Denmark, between 2000 and 2015. Methods The endometrium was evaluated by transvaginal ultrasound examination and office mini-hysteroscopy with biopsies in all non-hysterectomized women. Data regarding subsequent hysterectomy or endometrial sampling were obtained from medical records and the Danish Pathology Registry (Patobank). Results A total of 15 women were diagnosed with atypical hyperplasia or carcinoma during follow-up. Concurrent atypical hyperplasia or carcinoma was seen in 2.9% (3/102), and among women who remained at risk for more than 3 months after initial diagnosis of non-atypical endometrial hyperplasia (n = 94), progression to atypical hyperplasia or carcinoma was seen in 13% (median follow-up 5.2 years, range 3.6 months to 15.1 years). Sixty-six percent of the women with progressive disease were diagnosed with atypical hyperplasia or carcinoma more than 1 year after initial diagnosis, but only two were diagnosed later than 5 years (5.2 and 9 years). Conclusions The risk of being diagnosed with atypical endometrial hyperplasia or endometrial carcinoma more than 5 years after an initial diagnosis of non-atypical endometrial hyperplasia seems to be low in Danish women. Specialized follow-up more than 5 years after diagnosis of non-atypical endometrial hyperplasia may not be warranted.