Introduction Work-related asthma (WRA) amongst asthmatic patients in worldwide country are about 15%–25%. In Thailand, there are at least 3 million asthmatics patients but there have never been a figure of WRA presented. This is the first study in Thailand where a proportion of WRA amongst asthmatic patients was figured.

Methods A descriptive study was performed. The samples of 523 asthmatic patients in the Easy Asthma Clinics were interviewed in order obtain information related to onset of asthma and suspected cause of asthma. Four questions related to WRA included:

• history of asthma symptoms which get well when away from work or on holidays

• history of asthma symptoms which get worsen during the working days

• evidence of the sensitising or irritant agents in workplace that have been previously studied causing WRA

• evidence of exposure to the sensitising or irritant agents in workplace that have been previously studied causing WRA.

Descriptive statistics was used for analysis of data.

Results The proportion of WRA amongst asthmatic patients was 16.3%. Of those with WRA, 69.0% were new-onset asthma (87.9% were occupational asthma (OA) and 12.1% were reactive airways dysfunction syndrome). The remaining of 31% was work exacerbated asthma. The top three defined occupations were those working in the manufacturing, ground cleaning/waste management services and personal care and services, respectively. Considering the agents, top three agents were chloramine, metal fume and wood dust, respectively.

Conclusion The current study showed a similar result reported elsewhere where 16.3% of asthmatic patients were WRA and as expected, OA contributed most. This finding encourages physicians to explore patients’ occupation and their job descriptions since they will help physicians to focus on WRA. Therefore early recognition of early-onset of WRA will help curing or improving asthma at last.