Wrist extension is essential in the development of motor skills in young children. Adequate wrist extension is important for good grip function of the hand, as a slightly extended wrist results in a better and stronger grip. This retrospective study reviews the transfer of the flexor carpi ulnaris (FCU) or flexor carpi radialis (FCR) to the extensor carpi radialis brevis (ECRB) and/or longus (ERCL) to reconstruct wrist extension in 19 patients with obstetric brachial plexus palsy (OBPP). The average age at surgery was 7.2 (range 4–18) years. The mean follow-up was 3 years. Preoperatively, none of the patients had active wrist extension, with an average wrist extension-lag of 37.4 (SD 15.1) degrees. Postoperatively, average active wrist extension was 9.2 (SD 25.5) degrees. Average gain in wrist extension was 46.6 (SD 28.2) degrees, however individual gain varied substantially, i.e. between 0 and 100 degrees. Two patients were unable to reach the neutral wrist position postoperatively and in two patients wrist extension did not increase. The results of the tendon transfer to provide improvement of wrist extension in OBPP were satisfactory in most patients.