Intra-annual radial cracks in conifers have a major impact on the quality of wood. However, the exact cause of their formation is still unclear. Some authors have proposed summer drought as the main cause of these cracks, whereas others have proposed winter desiccation. Wood from Picea abies trees grown at different sites in Europe (Italy, Switzerland and Sweden) was analysed. Radial cracks always occurred within one tree ring. Tree rings with lower earlywood density had a higher number of radial cracks. Combining the results from different sites, evidence was found that cracking occurred during severe summer droughts, characterized by high water deficits, probably because the hydrostatic tension within the tracheids exceeded the fracture limits of the middle lamella. According to these observations cracks may occur after a drought in any tree ring located in the sapwood that is characterized by a low earlywood density, with the exception of the outermost one. In conclusion, cracks cannot be used to date drought events at an annual resolution.