Gastrointestinal symptoms have a prevalence of 20-40% in the general adult population in the Western world. These symptoms are generally considered to be poor predictors of organic findings [e.g. peptic ulcer disease (PUD) or malignancy]. Approximately 50% of patients seeking care for such symptoms have no organic explanation for these upon investigation. When other organic or other functional conditions are excluded [e.g. PUD, gastroesophageal reflux disease (GERD), irritable bowel syndrome (IBS)] the remaining patients are labelled as having functional dyspepsia (persistent or recurrent pain and/or discomfort centred in the upper abdomen). Management of functional dyspepsia remains a challenge, reflecting the heterogeneity of the patients and the uncertain role of drug treatment. Also, prognostic factors for treatment success are largely unknown. I have therefore performed a series of studies to shed light on these issues: The first study (Paper I) was performed in a randomly selected adult population (n=1,001) assessing upper and lower gastrointestinal symptoms at two occasions with 1 to 6 month intervals. The results show that gastrointestinal symptoms are common (57%) and fluctuate to some extent in the shorter term. Troublesome dyspeptic symptoms remain in two out of three individuals. This proportion was similar whether or not organic findings were present. In the second study (Paper II) 799 patients with dyspeptic symptoms were evaluated with regard to whether gastrointestinal symptoms, identified by self-administered questionnaires, correlate with endoscopic diagnoses and discriminate organic from non-organic (functional) dyspepsia. The impact of dyspeptic symptoms on health-related well-being was also evaluated. Approximately 50% of these dyspeptic patients were found to have functional dyspepsia at upper endoscopy. A difference was discovered in the symptom profile between patients with organic and functional dyspepsia. Predicting factors for functional dyspepsia were found. This study shows that use of self-administered symptom questionnaires may aid in clinical decision making for patient management, e.g. by reducing the number of endoscopies, although probabilities of risks for organic dyspepsia are difficult to transfer to management of the individual patient. The results also indicate that the health-related well-being in patients with functional and organic dyspepsia is impaired to the same extent, illustrating the need for effective treatment of patients with functional dyspepsia, a group not well served by currently available treatment modalities. The aim of the third study (Paper III) was to develop and evaluate a selfadministered questionnaire focusing on upper abdominal and reflux complaints to allow for identification of patients with heartburn and factors that might predict symptom relief with omeprazole both in GERD and functional dyspepsia patients. The diagnostic validity of the questionnaire was tested against endoscopy and 24-hour pH monitoring. The questionnaire had a sensitivity of 92%, but a low specificity of 19%. Symptom relief by omeprazole was best predicted by the presence of predominant heartburn described as ‘a burning feeling rising from the stomach or lower chest up towards the neck’ and ‘relief from antacids’. These results indicate that this questionnaire which used descriptive language, appeared to be useful in identifying heartburn and predicting responses to omeprazole in patients with upper gastrointestinal symptoms. The fourth study (Paper IV) was a pilot study investigating the symptom response to omeprazole 20 mg twice daily or placebo for a duration of 14 days in 197 patients with functional dyspepsia. We concluded that a subset of patients with functional dyspepsia, with or without heartburn, would respond to therapy with omeprazole. In the final study (Paper V) the aim was to identify prognostic factors for the treatment success to a 4-week course of omeprazole 10 or 20 mg once daily in 826 patients with functional dyspepsia. The most highly discriminating predictor of treatment success was the number of days without dyspeptic symptoms during the first week of treatment. Fewer days with symptoms during the first week indicated higher response rates at four weeks. In addition, positive predictors of treatment response to omeprazole were identified as age >40 years, bothersome heartburn, low scores of bloating and diarrhoea, history of symptoms for <3 months and low impairment of vitality at baseline. The results indicate that early response during the first week to treatment with a proton pump inhibitor seems to predict treatment success after four weeks in patients with functional dyspepsia. Conclusion: These studies have shown that a large proportion of adult individuals in society, both those who seek and those who do not seek medical care, suffer from symptoms located in the upper part of the abdomen regardless of whether an organic cause is present. A subset of patients without organic findings and other functional conditions, i.e. functional dyspepsia, respond to therapy with omeprazole irrespective of the presence or absence of heartburn . An excellent way to predict the response to a full course of omeprazole in functional dyspepsia is to assess the early response (first week) to treatment. These findings allow for better and faster targeting of acid inhibitory therapy in functional dyspepsia, which potentially can result in more effective clinical management of these patients and savings of health care resources.