In preparation for a national control programme acute respiratory infections (ARI) were studied in children under five years of age in 14 health centres, one referral and four district hospitals in five regions of Tanzania. 10.5% of all under-fives attending these health institutions presented with symptoms of ARI. 50% of all ARI patients were less than one year old. Cough, fever and difficult breathing were the main complaints motivating consultation. On examination nearly half of ARI patients had signs of difficult breathing, which corresponded to high prevalence of pneumonia (36.8% of all diagnoses). An excessive use of antibiotics for the treatment of all kinds of ARI was observed. This may explain the low case fatality rate of 2.6% for pneumonia. Those children who died from ARI came later to the health facility, had poorer nutritional status and more severe signs on examination than those children who survived. To reduce ARI mortality further, intervention should concentrate on early diagnosis and treatment at lower, i.e. dispensary and community levels.