Despite the diversity of surgical options for slipped capital femoral epiphysis (SCFE), there is an ongoing search for the technique that would ensure a satisfactory outcome, stable fixation of bone fragments and a low rate of complications. The aim of this study was to improve the surgical technique for SCFE in patients with moderate and severe SCFE. The study included 52 children (16 girls and 36 boys) aged 10-15 years (the mean age was 13.2 years) with chronic severe (Krechmar’s stage III) stable (according to Loder’s classification) SCFE. The control group (n = 16) underwent a classic Imhauser procedure; the main group (n = 36) underwent a triplane osteotomy proposed by the authors of the study. The patients were examined prior to surgery and in the late follow-up period (the mean follow-up time was 4.7 years, ranging from 1 to 10 years). The procedure included a clinical examination, history taking, radiography to measure the slip angle and the severity of the slip, and the Harris hip score to assess hip function. After 4.7 years, both groups demonstrated an increase in the range of motion, in comparison with their preoperative results (p ≤ 0.05), good Harris hip scores (94 points in the main group and 81 points in the control group. Postoperative radiographs showed consolidation of the bone, recovery of the proximal femur anatomy. Leg length discrepancy improved significantly in both groups. The proposed technique for extraarticular osteotomy allows recovering the length of the affected leg, the anatomy and physiology of the hip joint, is simple and less traumatic.