A randomized telephone survey on the practice of self-medication in the preceding 2 weeks was carried out from October 1989 to April 1990 among Chinese living in Hong Kong. 1068 people were interviewed. Self-medication was a common and universal practice by Hong Kong Chinese with a prevalence of 32.5% in 2 weeks. Those who reported illness were significantly more likely than those who did not use self-medication (65 vs 18.2%) and to have used more than one item of medications (39 vs 20%). Chinese tonics were the most frequently used self-medications although they were the least known. Chinese medicines were used as often as Western medicines in the self-treatment of illnesses. People used self-medication mainly because they felt that they knew what to do. About 80% of the Western and Chinese medicines were perceived to be effective but only 49% of the tonics were reported so. Side effects were reported from all types of medications with an overall prevalence of 6.4%. There was a lack of knowledge of the possible side effects in over 96% of the self-medications which is an area for patient education. The popularity but the relative lack of knowledge of Chinese tonics call for more scientific research and better regulation on their sales.