It has been suggested that warm and humid weather is related to a high incidence of Legionnaires' disease (LD), but no data on this association existed in The Netherlands. The objective of this study was to investigate the short-term effects of the weather on LD in The Netherlands. National LD surveillance and meteorological data were obtained. We analysed the data using Poisson regression, adjusting for long-term trends, and using principal components analysis. The highest weekly incidence of LD occurred when the mean weekly temperature was +17.5 degrees C. Mean weekly relative humidity, temperature and precipitation intensity were associated with LD incidence in the multivariable model. Warm, humid and showery summer weather was found to be associated with higher incidence of LD in The Netherlands. These results may be used to predict an increase in the number of cases of LD in The Netherlands during the summer.