Asthma and allergic disease in children is increasing in many Western countries but such trend has not been well-defined in Chinese populations. This paper aims to determine the prevalence of asthma and allergic disease in Hong Kong schoolchildren and compare it with previous data to identify a changing trend. We studied 4,665 schoolchildren aged 13-14 yrs using the International Study of Asthma and Allergy in Childhood (ISAAC) protocol to determine prevalence rates for asthma, wheeze, respiratory symptoms, rhinitis and eczema in 1994-1995. Additional questions on education levels of the parents and smoking status were also asked. Concordance between responses to the written and video questionnaires was good (76% for wheeze ever, 80% for current wheeze). Prevalence rates for asthma ever, wheeze ever, and current wheeze were 11, 20 and 12%, respectively, and were greater in boys (p < 0.05). Rhinitis affected slightly over half of the subjects (52%), and eczema was reported by a sixth (15%), whilst current rhinitis and current eczema were present in 44% and 3.6% of children, respectively. In multiple logistic regression: odds ratio male sex (OR) 1.47; (95% confidence interval (95% CI) 1.15-1.86); current rhinitis (OR 3.00; 95% CI 2.36-3.81); current eczema (OR 2.34; 95% CI 1.40-3.93); and active smoking (OR 2.00; 95% CI 1.38-2.89) were associated with current wheeze; whilst severe wheezing attack was associated with: current rhinitis (OR 2.72; 95% CI 1.47-5.02); current eczema (OR 6.13; 95% CI 2.82-13.33); and active smoking (OR 4.62; 95% CI 2.43-8.76). Age, parental education and passive smoking were not important factors. When compared to previous epidemiological data obtained in 1992, the prevalence rates for asthma ever and wheeze ever had increased by 71 and 255%, respectively, in Hong Kong schoolchildren. The severity of asthma and respiratory symptoms showed a similar increasing trend. Further studies should aim to identify the role of the environment in the pathogenesis of asthma.