A long-term follow-up of 49 patients with an average age of 38 years (range: 25-67 years) who had experienced infantile Blount's disease was done. Thirty-seven patients had bilateral disease, giving a total of 86 affected knees. Thirty-eight knees had conservative or no treatment during childhood; 13 were treated by epiphysiodesis, and 35 by osteotomy. At follow-up, 11 knees showed arthrosis, and 9 were graded as mild. Ten knees had been surgically treated by medial meniscectomy at an average age of 29 years (range: 19-45 years), after the diagnosis of Blount's disease. Four of the knees showed arthrosis. Most of the patients had a straight leg and mild or no pain from their knee. It is concluded that most children with infantile Blount's disease will, at the age of 40 years, have a straight leg without arthrosis and that one third can reach this result without any treatment.