Abstract: Quercus robur decline is a widespread phenomenon in northwestern Italy. In order todetermine the incidence, the severity and the evolution of the decline, Q. robur crowntransparency was assessed starting from 2007 in 11 study sites. In 2007, the mean crowntransparency ranged from 35% to 74% depending on sites. No significant variation was observedamong crown transparency levels in the 3 sampling periods (2007-2008-2009) at any sites. Soiland climate conditions of study sites were investigated in order to find possible correlations withcrown transparency. Drought in spring may be the main factor triggering off oak decline innorthwestern Italy. Ongoing experiments indicate that the availability of water and light mayhave effect only in the medium and long time period.