To investigate the effect of hot and cold temperatures on ambulance attendances. Design: An ecological time-series study. Setting and participants: The study was conducted in Brisbane, Australia. The authors collected information on 783 935 daily ambulance attendances, along with data of associated meteorological variables and air pollutants, for the period of 2000e2007. Outcome measures: The total number of ambulance attendances was examined, along with those related to cardiovascular, respiratory and other non-traumatic conditions. Generalised additive models were used to assess the relationship between daily mean temperature and the number of ambulance attendances. Results: There were statistically significant relationships between mean temperature and ambulance attendances for all categories. Acute heat effects were found with a 1.17% (95% CI 0.86% to 1.48%) increase in total attendances for 18C increase above threshold (0e1 days lag). Cold effects were delayed and longer lasting with a 1.30% (0.87% to 1.73%) increase in total attendances for a 18C decrease below the threshold (2e15 days lag). Harvesting was observed following initial acute periods of heat effects but not for cold effects. Conclusions: This study shows that both hot and cold temperatures led to increases in ambulance attendances for different medical conditions. Our findings support the notion that ambulance attendance records are a valid and timely source of data for use in the development of local weather/health early warning systems.