ObjectiveTo investigate the diagnosis and treatment of thumb polydactyly with symphalangism in children.MethodsSeven cases of thumb polydactyly with symphalangism were treated between January 2013 and May 2017. There were 5 males and 2 females, aged from 10 months to 11 years, with an average age of 3.1 years. The thumb-polydactyly was diagnosed with MRI and it was seen that the base of radial multi-finger and the proximal phalangeal joint were connected by cartilage. All patients were treated with resection, lateral collateral ligament reconstruction, bone osteotomy and internal fixation.ResultsThe operation was successfully completed, and there was no early complications such as infection and flap necrosis. All patients were followed up 6-23 months (mean, 14.1 months). At last follow-up, there was no deformity finger, scar contracture, and other complications. The extension of the interphalangeal joint was no limited, and the flexion range of the interphalangeal joint was 20-75° (mean, 56.7°). The appearance and function of the thumb was rated as excellent in 3 cases and good in 4 cases by Japanese Society for Surgery of the Hand (JSSH) scoring, with the excellent and good rate of 100%.ConclusionThe thumb polydactyly with symphalangism in children can be combined with clinical manifestations, X-ray film, and MRI examination to diagnose, and can obtain satisfactory results through the reconstruction of lateral collateral ligament, bone osteotomy, and internal fixation.