Abstract: In the present study we investigated the existence of duodenal ulcer activity monthly changes and clarify the roles played by gender, age and Helicobacter pylori We performed a hospital based cross sectional study of 939 patients with an incident duodenal ulcer out of 4339 dyspeptic patients from April 2004 to March 2006 in Baqihyatollah University of Medical Sciences, Tehran, Iran. On endoscopy two biopsy specimens were taken from antral gastric greater curvature within approximately 3 cm from the pylorus for rapid urease test. The number of duodenal ulcers and percentage of HP infection with regard to the time of evaluation were analyzed. There was a significance increase in the occurrence of duodenal ulcer in cold period of the year (autumn and winter), (p< 0.0005, χ2 = 18.1), After applying adjustment for age, gender and the year of evaluation, there was Also an increment in the percentage of HP infection in cold period of year in comparison to hot one (spring and summer), (p = 0.009, Odds ratio = 1.6, 95%CI 1.1-2.3). The present findings indicate that the observed duodenal ulcer occurrence increment in some cold months of the year was a manifestation of the cold month`s increments in percentage of HP infection diagnosis in dyspeptic patients who come to our center. For clarification of the biological basis of this phenomenon, further studies, including the interactions of climate, HP and neuroendocrine transmitters and usage of a reliable diagnostic method capable of distinguishing recent from old HP infection may be required.