Between 1982 and 1994 28 patients were treated for acute lateral knee ligament injuries; 25 patients, with a median age of 25.5 (range 16–75) years at injury, appeared for follow-up. Seven patients had isolated injury of the lateral collateral ligament/capsular structures, the remaining 19 patients had concomitant ligament injuries in the knee. Eight patients were treated conservatively, 1 with plaster immobilization and 7 with early mobilization. Eighteen patients underwent surgery, 17 of these within 3 weeks of injury. Repair/reconstruction of the cruciate ligaments was done at the same time as the lateral collateral ligament repair in 10 patients. At follow-up after a median of 7.5 years (range 6 months to 13 years), 11 had no varus instability, 7 had 1+, 5 had 2+, and 2 patients had 3+ varus instability. All patients with a final result of 2+ or 3+ had combined ligament injuries. The surgically treated lateral collateral ligament injuries all had a primary instability of 2+ or more. These patients showed an improvement in varus instability from a mean of 2.83+ preoperatively to a mean of 1.17+ postoperatively. Two-thirds of the surgically treated patients were stable or had a 1+ instability at follow-up. One conservatively treated patient with a 2+varus instability and 1 with 1+ showed no improvement. Five conservatively treated patients with initial varus instability of 1+ were stable at follow-up. One patient with a 1+ varus instability had anterior cruciate ligament (ACL) rupture. He had a primary ACL reconstruction without lateral repair. He had no varus instability at follow-up. Our study supports the notion that operation performed at an early stage in fresh injuries with a varus instability of 2+ or more gives improved stability as a final result. Conservative treatment may not be expected to give an improved stability, but is sufficient in mild varus instability (1+) without additional cruciate ligament injuries.