BACKGROUND: Little is known about the role of Chlamydia pneumoniae in the aetiology of acute respiratory tract infections (ARI) in children in developing countries. AIMS: To obtain better information, we studied the presence of C. pneumoniae and its association with clinical signs and symptoms of ARI in children under 5 years of age in The Gambia. METHODS: C. pneumoniae was sought by polymerase chain reaction in nasopharyngeal secretions and/or lung puncture aspirates from 324 infants under 3 months of age and 325 children between 3 months and 5 years of age with malnutrition, with or without pneumonia, and in control children. Clinical signs and symptoms for ARI and the spectrum of other viral and bacterial organisms were compared between those positive for C. pneumoniae and those negative. RESULTS: Of 324 young infants, ten (3.1%) showed the presence of C. pneumoniae whereas in the older children 50 of 325 (15%) were positive for C. pneumoniae. There was no significant association between clinical signs and symptoms of ARI and C. pneumoniae positivity in the young infants. Among older infants and children, there was a trend to more frequent lobar alveolar changes in those positive for C. pneumoniae. No bacterial pathogens were found to be significantly associated with C. pneumoniae infection. However, there was an association with measles in the malnutrition group and with RSV in the young infants group. CONCLUSIONS: In this study, C. pneumoniae was not associated with any particular clinical syndrome. We found no evidence that the organism plays a major role in ARI in young children in developing countries such as The Gambia.