BACKGROUND: The incidence of end-stage renal disease is especially high in men, and some studies indicated that smoking is a risk factor for men only. We investigated associations between obesity, smoking, and physical inactivity and chronic kidney disease (CKD) in the general population and whether risk for CKD was restricted to men. METHODS: This was a cross-sectional health survey of the entire adult population of Nord-Trondelag County, Norway, 1995 to 1997, with a 70.6% participation rate. Glomerular filtration rate (GFR) was estimated in all subjects 20 years and older from calibrated serum creatinine levels by using the simplified Modification of Diet in Renal Disease Study formula, and CKD cases are defined as those with a GFR less than 45 mL/min/1.73 m2 (< 0.75 mL/s). RESULTS: A total of 30,485 men and 34,708 women were included, and prevalences of GFR less than 45 mL/min/1.73 m2 (< 0.75 mL/s) were 0.8% and 1.1%, respectively. Age- and sex-adjusted logistic regression analyses showed dose-response relations for body mass index, smoking history, and physical activity. Relative risks were 1.77 (95% confidence interval [CI], 1.47 to 2.14) for obesity (body mass index > or = 30 kg/m2), 1.52 (95% CI, 1.13 to 2.06) for smoking (> 25 pack-years), and 2.14 (95% CI, 1.39 to 3.30) for physical inactivity (no or some physical activity in leisure time). For subjects with all these risk factors, relative risk was 5.10 (95% CI, 2.36 to 11.01). These results remained significant after adjusting for other known risk factors. No biological interactions between sex and obesity, smoking, or physical activity were found. CONCLUSION: Obesity, smoking, and physical inactivity were associated significantly with CKD. Men were not more susceptible to these risk factors than women.