['Although 2% to 4% of the population develop gastroesophageal reflux disease (GERD) annually, factors associated with the onset of GERD are scarcely known.', 'To assess whether such factors include weight gain and psychological distress.', 'Two cohorts (first: N=222; second N=754) drawn from 2 case-control studies were followed up for around 5 years. In 2004, all participants were directly interviewed using a validated questionnaire to collect data on body weight, height, GERD symptoms, and psychological distress. In 2009 to 2010, these same participants were again interviewed using the same methodology.', 'The response rate was 83.3% in cohort 1 and 39.1% in cohort 2, after a follow-up of 4.3±0.7 and 5.6±0.3 years, respectively. The multivariate analysis showed only weight gain and psychological distress as being independently associated with the onset of GERD in both cohorts. Weight gain per kilogram showed an adjusted odds ratio (OR) of 1.21 (1.01-1.44) in the first cohort, and a gain of 5 kg or more showed an adjusted OR of 4.65 (1.72-12.53) in the second. Somatization scores showed an adjusted OR of 1.09 (1.04-1.15) in the first cohort (measured as Minnesota Multiphasic Personality Inventory 2 hypochondriasis score) and 2.88 (1.04-8.02) in the second (measured as psychosomatic symptoms score). Body mass index on attaining overweight or obese status was associated with the onset of GERD in the unadjusted but not in the adjusted analysis.'] Are weight Gain and Somatization Associated With the Onset of Gastroesophageal Reflux Diseases : Results of Two 5-year Follow-up Studies?