Mercury intrusion porosimetry (MIP) is a widely used technique for characterizing the distribution of pore sizes in cement-based materials. It is a simple and quick indirect technique, but it has limitations when applied to materials that have irregular pore geometry. The relationship between MIP results and the actual pore distribution and connectivity can be better understood with the use of image analysis. This paper discusses the use of MIP to describe the pore structure of cements and the efforts to validate the technique with microscopy. In particular, a study using molten Wood's metal as an alternate intrusion liquid that is solid in the pores at room temperature and can be examined by scanning electron microscopy will be presented. Results of the image analysis and the intrusion behavior of Portland cement mortars will be discussed.