A survey on the use of antibiotics purchased through retail pharmacies was conducted in the Badinh district of Hanoi, Vietnam. The survey found that purchasers visit a pharmacy when they or those who felt they needed antibiotics had minor symptoms such as cough (34.1%), sore throat (32.5%), stomach upsets (10.0%) and diarrhoea (8.8%). The most often purchased antibiotics were ampicillin (31.1%), amoxyllin (16.7%), cotrimoxazol (11.6%), tetracycline (5.2%) and cephalexin (4.8%). The median of the purchased quantity was 10 tablets, the mean 11.34 tablets (95%CI 9.65-12.97). About 30% of the purchasers intended to take antibiotics for three days or less. The mean cost of a antibiotic purchase was US$1.27 (95%CI 1.06-1.39). The main reason for not taking a full course of antibiotics was not economic constraint, but the purchasers' poor knowledge about antibiotics. Logistic regression analysis indicates that age of purchasers, length of symptoms and kinds of treatment used before visiting a pharmacy could be used as predictive variables for the decision to buy antibiotics in preference to alternative drugs. Antibiotics are used when illness lasts longer than one week and antibiotics have not yet been taken. Antibiotics are also purchased by young rather than old people. The study documents the need for better health education about the rational use of antibiotics in the general public.