The expected direct and indirect costs following a fresh fibular rupture of the capsular ligament, and hence the socioeconomic burden on the patient, was investigated by a prospective randomised study comprising 120 males and females between 18 and 45 years of age. A comparison of three different conservative treatment methods A (immobilisation in a plaster cast for three weeks, followed by mobilisation with the aircast splint), B (mobilisation with the aircast splint) and C (Unna's paste dressing for two weeks with subsequent tape dressings and in each case immediate mobilisation) showed a significantly better stability after 6 months in the groups B (2.6 +/- 2.3) and C (3.6 +/- 3.8) than in A (4.8 +/- 3.5). The direct subsequent costs were also significantly lower in the groups B (DM 175.-) and C (DM 206.-) than in A (DM 340,-). Taking an average daily hospital care fee of DM 319.- (1991 in West Germany) as basis, the direct costs sequential to early functional treatment are the lowest also in comparison with surgical treatment in a hospital. The indirect sequential costs due to loss of working hours are mainly dependent on professionally conditioned physical stress but increase with the period of immobilisation after a fresh fibular rupture of the capsular ligament.