OBJECTIVE This study aims to evaluate the outcomes of mild and moderate slipped capital femoral epiphysis (SCFE) treated with in situ pinning. METHODS Eighteen hips of 15 patients (11 boys, 4 girls; mean age 12 years; range 9 to 15 years) with chronic stable SCFE were treated with in situ pinning. Immediate immobilization and internal fixation were applied. The results were evaluated according to Heyman Herndon's clinical and Boyer's radiologic classification system. RESULTS The mean follow-up was 56 months. The mean slipping angle was 38°, while the mean body mass index was 26 kg/m2. The mean preoperative hip flexion, internal and external rotation were respectively 94°, 9°, 59° and the mean postoperative hip flexion, internal and external rotation were 120°, 28°, 56°, respectively. The results were completely successful according to the Heyman Herndon's clinical and Boyer's radiologic classification system. The Trendelenburg test was negative in all patients. There was an asymptomatic CAM-type femoroacetabular impingement in one case, while history of femoral shaft fracture treated with surgically in the SCFE side and limb length discrepancy in one case. CONCLUSIONS In this study, we obtained successful clinical and radiological results of fixation with in situ pinning in patients with chronic stable mildly or moderately slipped capital femoral epiphysis without reduction. There were no clinical signs related to arthrosis and impingement syndrome in mid-term follow-up.