Aim. The objective of the present study was to estimate the effectiveness of the surgical correction of hyperfunction of the inferior oblique muscle in the children depending on the degree of overaction. Materials and methods. We undertook the analysis of hyperactivity of the inferior oblique muscle in 78 children (128 eyes) at the age varying from 4 to 15 years. All the patients were followed up for 9 years. The ophthalmological examination included the determination of vertical deviation with the use of the Hirschberg test and prisms, the study of eyeball movements in 8 gaze directions, the Bielschowsky darkening wedge test, the assessment of the character of vision by means of the Worth's four-dot test, visiometry, dioptos copy, and ophthalmoscopy. Results. The patients underwent myotomy, anterior transposition or myoectomy of the inferior oblique muscle with recession taking into consideration the degree of hyperfunction. Conclusion. Myotomy eliminates vertical deviation only in case of grade 1 overaction. Anterior transposition of the inferior oblique muscle provides an efficient tool for the surgical treatment of the condition being considered because it permits to rapidly correct the large angle of vertical strabismus in the patients presenting with grade 2 or 3 hyperfunction of the inferior oblique muscle. It is recommended to treat grade 4 overaction my means of myoectomy with a recession of up to 10 mm.