Data from a general practice-based, case-control study on gastroenteritis and the pathogens related to this disease were used to study the association between specific pathogens and the infected patients' ages and symptoms. For comparison, the occurrence of these pathogens in control patients, stratified by age, also is presented. In children with gastroenteritis who were <5 years of age, rotavirus (in 21% of patients) and Norwalk-like virus (NLV; in 15%) were the most common pathogens. Among patients who were 5-14 years of age, Campylobacter species (in 16% of patients) and Giardia lamblia (in 10%) were the most common pathogens. In the older patients, Campylobacter species was also the most common pathogen (8% to 15% of patients). In addition, several symptoms in case patients were associated with specific pathogens. Blood in the stool was associated with infection with Campylobacter species. In patients with fever, Salmonella species, Campylobacter species, and rotavirus were detected relatively often. Vomiting was associated with NLV and rotavirus. This is the first study in The Netherlands and one of the first studies in the world that has investigated a broad range of pathogens recovered from an unselected population of patients who had consulted general practitioners because of gastroenteritis.