Although several pathogenetic factors have been identified in recent years, the etiology of peptic ulcer disease is yet unknown. During the past few decades several investigators have reported seasonal patterns in peptic and duodenal ulcer disease. A review of the literature reveals vast differences between studies with respect to the type and number of patients selected, diagnostic techniques, the number of examinations and the interval of time between each as well as the method of data analysis. Nevertheless, there is solid evidence to conclude that peptic ulcer disease is lower during the summer than the other seasons of the year. Although many investigators have reported peptic ulcer disease to be more common in the spring and/or autumn, the evidence based on group studies thus far is not persuasive. On the other hand, initial findings on a small sample of patients studied by endoscopy at frequent intervals over at least a one-year period suggest that the season of peptic ulcer disease is a characteristic of each individual patient. Some experience recurrence of disease only in the spring while others experience such only in the autumn. Studies utilizing protocols which call for frequent endoscopic examination at regular (3-month or less) intervals for at least a one-year period are likely to clarify aspects of the seasonality of peptic ulcer disease.