The relationship between immediate skin reactivity to common allergens and adult asthma is not well defined. We retrospectively evaluated the profile of allergen sensitisation to common environmental allergens in 666 adult asthma patients at an asthma clinic in a teaching hospital in Hong Kong. Four hundred and seventy-one asthmatics (70.7%) were atopic; there were more males than females, although the difference did not reach statistical significance. The skin test positively rate decreased significantly with age so that asthmatics aged 35 years and older were four to six times less likely to be atopic and eight to 12 times less likely to be allergic to Dermatophagoides pteronyssinus, compared with young asthmatics aged 15 to 24 years (P<0.001). Inhalant allergy was more common than food allergy and of the inhalants, indoor allergens, including house dust mite and cockcoach were more important than outdoor allergens. The allergens most frequently associated with positive skin tests were D. pteronyssinus (62.2%), D. farinae (60%), cockroach (40.7%), cat dander (24.0%), and royal jelly (16.8%). In conclusion, allergen sensitisation is common in adult asthmatics in Hong Kong, and allergen avoidance should be included as part of the preventive strategies for controlling the disease in the community.