AIM: To determine prevalence of H pylori infection in symptomatic children in Buenos Aires, Argentina, and to investigate factors associated with H pylori positivity.METHODS: A total of 395 children with upper gastrointestinal symptoms referred to the Gastroenterology Unit of the Children Hospital "Sor Maria Ludovica"were evaluated for the presence of H pylori by the 13C-Urea Breath Test (13C-UBT). A questionnaire was applied to the recruited population.RESULTS: Prevalence of H pylori infection was 40.0% in tlis population (mean age 9.97 ± 3.1 years). The factors associated with H pylori positivity were number of siblings (P ＜ 0.001), presence of pet cats (P = 0.03)and birds (P = 0.04) in the household, and antecedents of gastritis among family members (P = 0.01). After multivariate analysis, number of siblings [Odds ratio (OR)= 1.39; 95% CI, 1.20-1.61] and contact with pet cats (OR = 1.76; 95% CI, 1.00-3.09) remained as variables associated with H pylori infection.CONCLUSION: The prevalence of H pylori infection in children with upper gastrointestinal symptoms in Argentina was similar to that reported in developed countries. Children from families with a higher crowding index and presence of pet cats have a higher risk of being colonized with H pylori.