The purpose of this study was to evaluate the efficacy of vastus lateralis release for painful bipartite patella. We have also compared the results of open method versus arthroscopic method using a holmium:YAG laser system (OmniPulse Holmium Laser System; Trimedyne Inc, Irvine, CA).This study was a nonrandomized control and cross-over trial.Fifteen patients with 17 painful bipartite patella who underwent vastus lateralis release were included in this study. The average age of patients was 14.3 +/- 2.2 years. In 7 knees of 6 patients, vastus lateralis release was performed through a skin incision over the bipartite fragment, and in 10 knees of 9 patients, we performed the procedure arthroscopically with the holmium:YAG laser. We assessed clinical and radiographic data of the patients chronologically in both groups.In all patients, pain over the fragment disappeared within 4 weeks after the operation, and all returned to their previous sports activities at an average of 3.1 +/- 0.9 months postoperatively. Clinical assessment was classified as excellent in 13 knees and good in 4 knees. Bone union at 6 months after the operation was complete in 11 knees (64.7%) and incomplete in 6 knees (35.3%), and none of the knees was graded as not healed. Bone union in patients with an age of 15 or younger was significantly better than that in patients over 15 years of age (P <.05). Release under arthroscopy showed statistically better results in duration of knee effusion (P <.05), return of circumference of thigh (P <.05), and return of muscle strength (P <.05).Because vastus lateralis release is less invasive surgery with good results, we conclude that this procedure can be a first choice of operative treatment for painful bipartite patella.