Aims: Mainly due to insufficient numbers, former studies do not allow definite conclusions concerning the potential etiologic role of body weight and smoking to lumbar disc diseases. The aim of the present analysis of the large-scale case-control study "EPILIFT" is to further clarify this relationship. Methods: 564 (male and female) patients with lumbar disc herniation and 351 patients with lumbar disc narrowing (chondrosis) between 25 and 70 years of age were prospectively recruited in four study regions in Germany (Frankfurt am Main, Freiburg, Halle/Saale, Regensburg). 901 population control subjects were drawn from the regional population registers. In a structured personal interview, we elicited the mean body weight, body height and cumulative smoking amount until the date of first diagnosis. Odds ratios (OR) and 95% confidence intervals (CI) were calculated together for men and women using unconditional logistic regression analysis, adjusted for age, sex, region, cumulative lumbar load (caused by manual materials handling and activities with forward or sideward bending or torsion of the trunk), psychosocial workload, and unemployment as major life event (for disc herniation, only). For determining the association between body weight and smoking amount, respectively, and the workload the cumulative load on the lumbar spine of the total occupational life was considered. Cumulative lumbar load was quantified on the basis of the compressive force in the lower lumbar region for all handlings of objects weighing 5 kg or more and activities with trunk bending of 20 degree or more. Results: The results of this case-control study reveal a positive association between body weight and lumbar disc herniation as well as lumbar disc narrowing. The relationship is slightly more pronounced for lumbar disc herniation than for lumbar disc narrowing; for a body-mass-index of about 29 or more, disc herniation risk is doubled in comparison to a body-mass-index of less than about 22. There is a nearly additive interaction between body weight and occupational lumbar load. We do not find a clear dose-response relationship between smoking amount and lumbar disc disease: For a medium, but not for a high cumulative smoking amount the risk for a disc-related disease is slightly elevated. Conclusions: According to our multi-center case-control study, body weight is related to lumbar disc herniation as well as to lumbar disc narrowing. The additive interaction between overweight and cumulative lumbar load points to a common pathophysiological pathway (e.g. lumbar compression).