This study investigated seasonal variation in the incidence of spontaneous pneumothorax (SP) among young adults aged 15-44 years, in order to identify possible associations with meteorological parameters in a subtropical Asian climate. Neither particular months nor seasons of the year were significantly associated with the incidence of SP. BACKGROUND and OBJECTIVE: While links between meteorological conditions and the incidence of spontaneous pneumothorax (SP) have been postulated, the findings are controversial. In this first large-scale, nationwide, population-based study, seasonal variation in the incidence of SP among young adults aged 15-44 years was investigated, in order to identify possible associations with meteorological parameters (rainfall, ambient temperature, relative humidity, atmospheric pressure, hours of sunshine) in a subtropical Asian climate. METHODS: Data (2001-2005) from the National Health Insurance Research Database were used to identify a total of 8575 patients who had been hospitalized with a principal diagnosis of SP. The autoregressive integrated moving average method was used to evaluate the effects of seasonality and monthly climatic factors on the incidence of SP. RESULTS: The incidence of SP was not significantly associated with either particular months of the year or seasons. After adjusting for seasonality, month and time trends, relative humidity was positively associated with the monthly incidence of SP among men, while ambient temperature and rainfall were significantly associated with SP events among women. However, changes in monthly atmospheric pressure did not appear to influence the monthly risk of SP. CONCLUSIONS: These results do not support the premise that seasonal factors are involved in precipitating SP, although certain climatic parameters showed weak associations with the incidence of SP. Future studies should investigate other combinations of weather phenomena and potential triggering factors, in order to shed light on the occurrence of SP in various regions and climatic conditions, and among both men and women.