In a prospective, random study carried out at the Casualty Clinic of the University Hospital of Hannover from 15 April 1986 to 31 July 1986, 200 patients were randomly selected from four treatment groups, according to treatment: operative-immobilized (group A, n = 52), operative-functional (group B, n = 50), conservative-immobilized (group C, n = 48) and conservative-functional (group D, n = 50). Follow-up examinations were made in 92.5% of patients after 3 months and 64% after 12 months. At the 3-month and 1-year follow-ups, no statistically significant differences were found in the total evaluation (100-point checklist) Moderately significant instability (6 degrees -10 degrees talar tilt and 6-10 mm anterior talar dislocation) in the conservative groups C and D was observed only in the clinical-radiological instability test. This statistically significant difference is, however, only evident in stress tenographically confirmed dual-ligament lesions. No functional physiological differences can be found after 12 months; on average, the period of incapacitation is 3 weeks shorter than with primary functional treatment, but so far there are no long-term results. Until late results are available, we conclude that conservative treatment, even for professional athletes, can be recommended as the procedure most free of risk and most economical; if at all, operative therapy should only be carried out when the instability is very serious.