Inguinal hernias are very common disorders, especially in men, with inguinal herniorrhaphy being one of the most frequently performed general surgical procedures in men. Theoretically, obesity might increase the risk of groin hernia by increasing intra-abdominal pressure. The objective of the present study was to investigate whether overweight and obesity in middle age could significantly predict future groin hernia in men. Prospective cohort study; General population of men living in Gothenburg, Sweden; A community-based sample of 7483 men aged 47 to 55 years were followed-up from baseline (1970-1973) for a maximum of 34 years. A diagnosis of groin hernia according to the Swedish hospital discharge register. A total of 1017 men (13.6%) were diagnosed with groin hernia. An inverse relationship was found between body mass index (BMI) and risk of groin hernia. With each BMI unit (3-4 kg), the relative risk for groin hernia decreased by 4% (P < 0.0001). Compared with men of normal weight, obese men had a 43% lower risk (P = 0.0008, 95% confidence interval 21%-59%). Heavy smokers demonstrated a 26% lower risk for groin hernia (P = 0.003, 95% confidence interval 10%-39%). Diabetes, high physical activity, and blood pressure were not associated with groin hernia. Entering other variables potentially associated with groin hernia, as age, BMI, smoking, and serum cholesterol, in a multivariable analysis left the risk estimates for BMI and smoking virtually unchanged. In a large community-based sample of middle-aged men overweight and obesity were associated with a lower risk for groin hernia during an extended follow-up. Obesity, in comparison with normal weight, reduced the risk of groin hernia by 43%. A reduced risk of groin hernia was also noted in heavy smokers. Obviously, hernia may be more easily detected in lean men but a true protective effect cannot be excluded.