Aim. To give evidence of the effectiveness of non-surgical ultrasound treatment for complex pararectal fistulas.Materials and methods. A clinical and experimental non-randomized prospective study was conducted, based on data from 120 experiments on 16 dogs and the results of observation of 64 patients. The patented Proxon ultrasound surgical device was used. We studied impression-stamps on the 1st, 2nd, 5th, 7th, 9th and 11th days, as well as the histology of fistula tissues before and after treatment.Results. Use of the author’s method led to the purification of the fistulous canal from purulent necrotic masses and to regression of inflammation and a decrease in the level of neutrophils in the percentage in smears from fingerprints from 61.31±6.23 to 45.02±3, 59, macrophages from 3.89±0.75 to 1.91±0.57, as well as a significant increase in the number of fibroblasts from 1.05±0.45 to 5.33±1.11 to the fifth-seventh day. During histological examination, after courses of high-frequency ultrasound exposure, lysis of the epithelial lining of the fistulous canal, hypervascularization of the pathological focus, regression of inflammatory infiltrate, growth and maturation of granulations and fibrosis were registered.Conclusion. After three stages of treatment, recovery was registered in 85.94±4.35% of patients. Morphological studies confirmed the high efficiency of the innovative author’s method of non-surgical treatment for complex pararectal fistulas using the Proxon ultrasound surgical complex.