A cohort of 151 infants and young children aged 1-23 months from a poor peri-urban community of Bangladesh was studied to determine the relationship between Helicobacter pylori colonization and morbidity due to diarrhoea. A 13C urea breath test was performed to detect the presence of H. pylori. Children were followed up at home every alternate day for 6 months and diarrhoeal morbidity data were collected. Diarrhoeal morbidity was compared between H. pylori-positive and H. pylori-negative children. Sixty-eight (45 per cent) children were H. pylori positive and 83 (55 per cent) were H. pylori negative. During the first 1-month period following the breath test, three (4.4 per cent) H. pylori-positive and four (4.8 per cent) H. pylori-negative children had diarrhoea. Thirty-two (47 per cent) of the children in the positive group and 43 (52 per cent) in the negative group had one or more episodes of diarrhoea during the 6-month follow-up period. Median number of diarrhoeal episodes was 1.0 (range 1.0-4.0) in the H. pylori-positive children and 2.0 (range 1.0-5.0) in the H. pylori-negative children (p = 0.19). No significant difference was observed in the cumulative days with diarrhoea. The results of this study suggest that H. pylori colonization is not associated with diarrhoeal morbidity in infants and young children.