The aim of this study was to identify occupational activities important for the development of arthrosis of the knee, taking into account the confounding factors that were suspected or could be recognized. In the archives of the Department of Diagnostic Radiology at the Malmö University Hospital all radiographs of weight-bearing knees of patients with painful knee joints from the period 1982-1986 were reassessed. We found 340 probands, i.e., subjects with arthrosis of the knee of at least grade 1 in the Ahlback classification. These probands and their age- and sex-matched controls (680) were analyzed by a validated questionnaire for details of activities at work inducing knee moment over three 15-year-periods as well as their history of knee injuries at work or in their leisure time. The questionnaire was answered by 266 (79%) arthrosis probands and 463 controls (70%). The results of the questionnaire answers and of the recorded history of knee injuries were statistically analyzed by logistic regression. The relative risk of knee arthrosis was slightly increased (RR: 1.9; CI: 1.4-2.7) in probands with weight-bearing knee bending, i.e., dynamic load of the knee joint when bending, whereas knee injuries (meniscectomies and haemarthrosis) were associated with a higher risk. Weight-bearing knee bending corrected for confounders was not a significant factor for knee arthrosis. Overweight was observed to increase the relative risk. A sedentary profession had, on the other hand, a low risk. The knee injuries (66) were, but for 9 probands, sustained in leisure activities, mainly soccer. We thus conclude that work which induces weight-bearing knee bending by itself does not significantly increase the risk of developing arthrosis of the knee - knee injuries and overweight are more important.