Previous studies concerning ruptures of the lateral ligaments of the ankle dealt with acute first ruptures. There are a few articles about chronic instability of the ankle but no prospective investigations have been reported concerning the treatment of recurrent ruptures. Good results were obtained following after non-operative treatment of acute ruptures of the fibular ligaments of the ankle joint. This prospectively randomized study was commenced to test whether recidivations of the rupture of the lateral ligaments can also be treated non-operatively or if they are in need of operative repair. The second question to be answered was whether these injuries should be treated differently depending on the treatment of the first rupture. From December 1986 to November 1989, 109 patients with a recidivation of a rupture of the ankle joint lateral ligaments were included in this prospective trial at the Department of Trauma Surgery, Hannover Medical School. They were divided into two groups depending on the therapy used to treat the first injury: The relapse was classified as a second-stage-rupture in cases where treatment of the first ligament rupture did not involve an operation and as a rerupture if the initial rupture was surgically repaired. Half of each group was treated randomly either with surgical ligament repair or without. A total of 100 patients (92%) at an average age of 24 years (11 to 49 years) was seen for follow-up examination one year after the relapse: The follow-up included the patient's subjective assessment, a clinical examination, and stress radiography. A 70 point score was used for evaluation of the total result. Two wound infections requiring reoperation were observed in the operative treatment groups. The follow-up examination revealed better results in both operative treatment groups (A and C), which was statistically significant (P < 0.05). Patients with a second-stage-rupture showed a significantly higher (P < 0.001) stability by stress radiography after surgical treatment (group A) in contrast to non-operative treatment (group B). In addition, the subjective and clinical results indicated a tendency towards better results which were not statistically significant (P < 0.09 and P < 0.07). In cases of rerupture the patient's subjective assessment revealed significantly more (P < 0.05) complaints after non-operative treatment (group D). Clinical results were comparable, and radiologic assessment showed a tendency towards higher joint stability after surgical treatment (group C), although it was not statistically significant (P < 0.07). Based on the results presented, the authors recommend the surgical repair of ankle joint ligaments in cases of second-stage- or rerupture.