Introduction. Forearm fractures are the second most common injuries to the locomotor system in children, after injuries to the distal forearm. Usually, pediatric forearm fractures occur due to indirect violence. In the treatment of forearm fractures in children, we aim to achieve union, correct length and axis of both forearm bones. Forearm fractures can be treated non-operatively, with casting, as well as operatively. In children, the most commonly used operative method is closed reduction and intramedullary stabilization using TENs. We cannot forget about complications during treatment. Aim. The aim of the study is to analyze the most common late complications of diaphyseal fractures of both forearm bones in children in relation to the treatment method. Material and methods. The study included 120 children aged 3-17 y.o., hospitalized in the Pediatric Orthopedics and Rehabilitation Clinic at the Medical University in Lublin in 2014-2018. The children were divided into 2 groups based on the type of diaphyseal forearm fractures. The analysis included the type and frequency of complications with regard to the treatment method. Results. The study groups consisted of 57 patients treated non-operatively-with casting and 63 patients treated operatively with flexible intramedullary nails. 24 girls and 33 boys were treated non-operatively. 13 girls and 50 boys were treated operatively. Among 61 patients treated non-operatively, 45 had no complications, 14 developed refractures, 1 had a delayed union, and 1 patient had a non-union. Among 59 patients treated operatively, 53 had no complications, 5 developed refractures, and 1 had a delayed union. The most common complication in both modalities was refracture. The complications of non-operative treatment were managed non-operatively in 10 patients and operatively in 4 patients. Operative treatment complications in 1 patient were managed non-operatively while 6 required repeat intramedullary fixation. Any form of treatment complications developed in every fourth patient who received non-operative treatment, while in the case of flexible intramedullary fixation, in every tenth patient. Conclusions. The method of management did not significantly influence the frequency of a specific complication. These complications were 2.5 times more frequent in non-operative treatment, compared to the operative method.