Objective: 1. To determine the association between heavy object lifting and occurrence of inguinal hernia in adult male 2. To identify the other risk factors of inguinal hernia in adult male Design: An unmatched case-control study. Setting: Three tertiary care hospitals-Bangkok Metropolitan Administration Medical College and Vajira Hospital, Phramongkutklao Army General Hospital and Phrapinklao Hospital. Method: Two hundred and nineteen patients were enrolled in this study, 73 patients as cases and 146 patients as controls. Cases were defined as newly diagnosed inguinal hernia in adult male with the duration of symptom less than one year. The corrected diagnoses were confirmed form operative report. Previously surgical repairs of inguinal hernia were excluded. Controls were male in-patients who were admitted during the same periods as cases. Controls were approximately age-matched within five years interval to cases. In-patients with urological, colo-rectal and cardio-thoracic diseases were not recruited as controls. Both cases and controls were asked to answer the same questions on their demographic background, past history of heavy object lifting, smoking, urinary outflow tract obstruction, constipation, chronic cough. Their height, estimated body weight before occurrence of the diseases and previous appendectomy via right lower abdominal incision were recorded. Result: In univariate and multivariate analysis, no association between all exposure variables and inguinal hernia were found. The adjusted odds ratio for inguinal hernia in relation to past history of heavy object lifting was 1.13 (95% Cl = 0.58-2.22). The adjusted odds ratio in relation to smoking, increased intra-abdominal pressure, previous appendectomy and obesity were 1.03 (95% Cl = 0.55-1.9), 1.05 (95% Cl = 0.59-1.9), 1.29 (95% Cl = 0.44-1.32) and 0.66 (95% Cl = 0.33-1.32) respectively. Conclusion: Risk effects of heavy object lifting, smoking, urinary outflow tract obstruction, constipation, chronic cough to inguinal hernia are always posted without adequately evidence supports. This study did not suggest an inverse effect between past history of heavy object lifting, smoking, increased intra-abdominal pressure, previous appendectomy and inguinal hernia.