Introduction: Both-bone forearm fractures in children can be treated non-operatively with a cast. Most previous studies have shown favourable outcome; however, information on the functional outcome after skeletal maturity is still scanty. Therefore, this study was conducted to determine the functional outcome after skeletal maturity in fractures with at least four years of growth remaining. Materials and Methods: This retrospective study was conducted from March 2012 until March 2013. Age at the time of fracture was taken as until 10 years for females and until 12 years old for males with at least four years of growth remaining. Fractures occurring in the diaphysis were included in the study. Functional outcomes were assessed at or after skeletal maturity. Results: Forty-four children fulfilled the criteria. The ages of the youngest and the oldest at the time of fracture was five and 12 years old respectively. Follow-up of the male and female patients were 7.4 years and 5.5 years respectively. There was a significant difference between post-reduction angulation and angulation at skeletal maturity of the radius and ulna (p<0.001). Out of 44 patients, 39 had excellent and five had good functional outcomes. No patient had fair or poor functional outcome. There was no association between the functional outcome and the angulation of forearm bones after skeletal maturity. Age at the time of fracture had a significant association with the functional outcome. Conclusion: Non-operative treatment of both-bone diaphyseal forearm fractures in a cast has good to excellent functional outcomes in children who still have four years of growth remaining.