BACKGROUND: In October 1995, over 50 cases of appendectomies among the 1.605 residents of the island La Désirade (Guadeloupe) were reported by the only island clinician to the local health authority. We describe the outbreak investigations which were implemented in order to describe the phenomenon and generate hypotheses on its cause. METHODS: An exhaustive case finding of residents having undergone appendectomy between 10 August 1995 and 22 July 1996 was conducted. We reviewed the medical charts of the cases; read pathology slides; interviewed cases and their families to retrieve detailed clinical history; studied the prevalence of markers of infection and of stool pathogens and analysed water supply quality data. RESULTS: We identified 226 cases of appendectomy (14% of the island population), 40% in May-June 1996, 46% in males and 40% under 15 years of age. Clinical, biological and pathological findings were heterogeneous and did not support the hypothesis of an outbreak of appendicitis. The study of abdominal symptoms in the families of the cases did not support person to person transmission but revealed frequent, subacute or chronic abdominal complaints. The analysis of markers of infection or of stool bacteria and parasites in a self selected sample of the island population was not suggestive. Water supply did not show any bacterial or chemical contamination. CONCLUSION: The investigation of a large outbreak of appendectomies was unable to find a single infectious or toxic origin to a high prevalence of chronic abdominal symptoms in an isolated population. An inappropriate medical answer in an isolated population probably turned heterogeneous complaints into an outbreak with major public health consequences.