To explore the relative contribution of cumulative physical workload, sociodemographic and lifestyle factors, as well as prior injury to hospitalization due to knee and hip OA.We examined a nationally representative sample of persons aged 30-59 years, who participated in a comprehensive health examination (the Health 2000 Study). A total of 4642 participants were followed from mid-2000 to end-2015 for the first hospitalization due to knee or hip OA using the National Hospital Discharge Register. We examined the association of possible risk factors with the outcome using a competing risk regression model (death was treated as competing risk) and calculated population attributable fractions for statistically significant risk factors.Baseline age and BMI as well as injury were associated with the risk of first hospitalization due to knee and hip OA. Composite cumulative workload was associated with a dose-response pattern with hospitalizations due to knee OA and with hospitalizations due to hip OA at a younger age only. Altogether, prior injury, high BMI and intermediate to high composite cumulative workload accounted for 70% of hospitalizations due to knee OA. High BMI alone accounted for 61% and prior injury only for 6% of hospitalizations due to hip OA.Our results suggest that overweight/obesity, prior injury and cumulative physical workload are the most important modifiable risk factors that need to be targeted in the prevention of knee OA leading to hospitalization. A substantial proportion of hospitalizations due to hip OA can be reduced by controlling excess body weight.