Abstract The microstructure of a medium density fiberboard (MDF) has attracted much interest, because it determines most of the properties during production as well as during use of this type of board. In this paper the sub-micrometer computer tomography (sub-µm-CT) with very high resolution was used in order to investigate an industrially produced MDF. The data obtained were analyzed using mathematical morphology and image analysis in order to obtain information on the distribution of voids and the fiber material. Resulting distributions were found to follow -law which was confirmed using the maximum likelihood estimation. Eventually, good correlations between void distribution and local density as well as between the proportion of cell wall material and local density were found in this investigation.