Background: (13) C urea breath test (UBT) results, used for the diagnosis of Helicobacter pylori infection, fluctuate in different age groups. We characterized both the age- and gender-based trends of UBT results, from early childhood through late adulthood., Methods: A national H. pylori referral laboratory was screened for all positive UBTs during 2007-2008, determined as a delta over baseline (DOB) ≥ 3·5. Data were analysed with respect to both age and gender., Results: In the studied period, 61,060 UBTs were performed and 24,237 were positive. After excluding multiple testing for an individual, a total of 21,767 positive results were analysed. The male/female ratio for positive UBTs was 1 : 1·77. DOB results decreased as age increased from a maximum of 38·6 ± 21 at age 3-5 years to 21·1 ± 12 at age 19-30 in females (P < 0·001) and from 30·0 ± 16 at age 6-10 years to 14·7 ± 8 at age 19-30 years in males (P < 0·0001). At this point, the values reached a nadir for both genders. In patients older than 60 years, old test results increased moderately (P < 0·003). In all age groups, except 6-10 years old, females had significantly higher UBT results than males., Conclusions: The decrease in mean UBT values already occurs during the first decade of life, and results increase following the sixth decade. Females have significantly higher results than males even in early childhood and throughout old age., (© 2011 The Authors. European Journal of Clinical Investigation © 2011 Stichting European Society for Clinical Investigation Journal Foundation.)