Some meteorological and geo-orographical factors related to cloud-to-ground flashes in Castilla-Leon (Spain) are studied. The relationship between flash density and the number of days with thunderstorms (thunderdays) is analysed, and a clear dependence and geographical variability is found. It is also shown that flashes have an average delay of four hours with respect to the time of the beginning of convection. The effect on flashes of dry static instability and moisture content is analysed by classifying days into four types according to the average values of the 850-700 hPa temperature difference and the 850 hPa dew-point temperature. A similar classification using the 700 hPa wind direction is used to analyse the effect of the mean-level flow on flashes. The results suggest that the daily number of flashes is mainly affected by the moisture content. Finally, a relationship between the cloud-to-ground flash density and geo-orographical factors (altitude, latitude and longitude) is deduced using multiple linear analysis.