External genital endometriosis is a widely spread disease among patients of reproductive age. Most of the hormonal drugs currently available for the treatment of this disease exclude pregnancy planning. Considering the off-label effects of vitamin D (anti-inflammatory, antiproliferative, antiangiogenic and immunomodulating), the use of cholecalciferol can be regarded as a promising and pathogenetically justified treatment for endometriosis. Material and methods. In the first stage, endometriosis was surgically induced in 39 female rats. Two weeks later, in the second stage, diagnostic laparoscopy was performed, after which all rats were divided into 4 randomly selected groups. The 1st group (A) (n=8) was given cholecalciferol orally for 3 weeks, with a daily dose of 2500 IU/kg. The 2nd group (B) (n=6) was given cholecalciferol orally for 3 weeks, with a daily dose of 5000 IU/kg. The control group (C) (n=13) was not treated, while the comparison group (D) (n=12), was treated with dienogest at a dose of 1 mg/kg daily orally for 3 weeks. In the third stage, autopsies of the rats were performed. Results. When using cholecalciferol, there was a either a steady regression or complete resorption of endometrioid foci. The effect was dose-dependent (complete resorption of endometrioid heterotopias was determined in 12.5—54.55% of observations, depending on the applied dose of the drug). The effectiveness of the cholecalciferol as a monotherapy on endometrioid foci in the experimental model was comparable with the effectiveness of dienogest.