One hundred and thirty eight knees of 124 patients with partial rupture of the patellar ligament were treated surgically after failure to heal them by conservative means. Ultrasonography was used to confirm the diagnosis in 45 knees, and when positive it had a good correlation with the operative findings. During surgery excision of the devitalized tissue in the patellar tendon was performed. Histologic examination of the removed tissue revealed degenerated, fibrotic tissue with neo-vascularization, and slight to moderate inflammation resembling devitalized tissue. The patients were re-examined 18.6 +/- 15.0 months post-operatively. Ninety-seven patients (111 knees = 80.4%) benefitted from the operation with excellent or good results. Thirteen knees had to be re-operated with more radical excision due to renewed symptoms. In conclusion, surgical excision of the devitalized tissues gives a good functional result in most of the cases in which non-operative treatment with rest and physical treatment has failed, helping the athlete to return to his pre-injury activities.