A radiological follow-up study of osteochondrotic lesions in the distal ulna was carried out in 58 Danish Landrace breeding sows for a period of 15 months (October 1992 to December 1993). This was part of a major project involving the radiological investigation of articular-epiphyseal and physeal development to investigate osteochondrotic lesions in pigs. The radiological lesions were graded from 1 to 5 with increasing severity. It was observed that not all pigs passed through all grades. Only 21% of the pigs had no radiological osteochondrotic lesions (grade 1) during the first radiography series. After 5-7 months, the number of pigs without osteochondrotic radiological lesions were observed to have increased dramatically (21-69%), but the converse was true for grades 2 (mild), 3 (moderate), 4 (severe) and 5 (very severe): (33-17%), (21-9%), (19-5%) and (7-0%) respectively. This was observed with increasing age and weight. The 3rd radiography series indicated that the percentage of pigs without osteochondrotic lesions increased up to 82%, and that grades 2, 3, and 4 had fallen to 14%, 2% and 2% respectively, while grade five remained at 0%. This indicated that the distal ulna osteochondrotic lesions can be important in breeding pigs during the period of growth before first pregnancy. During the first pregnancy the osteochondral ossification fault can be corrected, and the lesions heal. The ulna growth plates were not closed at the second, but mostly closing during the third radiography series.