Prevalence of childhood asthma is increasing worldwide including in developing countries such as Thailand. Despite a wide availability of epidemiological data on childhood asthma in Thailand, prevalence of asthma in adults has not been well studied within this community. Objectives of this study were to study prevalence of asthma, allergic rhinitis and eczema in a random group of university students in Bangkok using the standardized written and video questionnaires from the ISAAC phase I protocol. The ISAAC phase I, written and video (International version, AVQ 3.0) questionnaires were administered to 3631 randomly selected university students from six universities in Bangkok. The age range of subjects were between 16-31 years (mean +/- SD= 19.1 +/- 1.7 years). There were 1197 males and 2434 females (ratio = 1:2.03). Data were entered into and analysed by the EpiInfo 4 program. Prevalence of wheeze within the past 12 months and of diagnosed asthma for this group of subjects was 10.1% and 8.8%. Prevalence of allergic rhinitis (nasal with eye symptoms within the past 12 months) was 26.3% and of eczema (rash at typical sites of atopic dermatitis, within the past 12 months) was 9.4%. Presence of rhinoconjunctivitis, gender and age were significant risk factors for asthma with male, younger subjects and those with rhinoconjunctivitis reported more frequent asthma-related symptoms (P < 0.01). As in previous studies which found an increase in asthma among Thai children, this survey indicates that the prevalence of asthma among Thai university students has increased to the same level as in several European countries. A large number of adults residing in Bangkok are suffering from rhinitis-related symptoms, the majority of which probably represents allergic rhinitis.