The aim of this study was to evaluate the number and location of annual growth units (GU) in Norway Spruce logs to have an information on the past growth of trees and thus a better knowledge of wood properties like density and knottiness. Two devices were used: an optical device which gives an accurate, description of the external log shape and a medical CT scanner which, in addition, gives information about the internal density of log. For each device, a specific method was developed to detect annual GU. The "optical method" was based on variations of the cross-section surface along the logs and the "X-ray method" on variations in the density profile. The optical method provided an accurate evaluation of the number of GU. The "X-ray method", more sensitive to the presence of lammas shoots, generally overestimated the number of GU but provided a very good location of knotty areas inside the logs.