This clinical report describes the situation of a patient who was concerned about the appearance of porcelain crowns that were placed on the maxillary incisors 4 years prior. The mechanicochemical gingival retraction technique combining the use of ferric sulfate and knitted retraction cord is described as a possible etiology of internalized discoloration of the dentin in this situation. The hypothesis is explained by the high acidity of gingival retraction fluids (GRFs) and the high affinity of iron for hard tooth tissues, resulting in an interaction with bacterial byproducts and precipitation of insoluble ferric sulfide in the porous demineralized dentin. A prospective clinical trial is warranted to track the effects of GRFs on tooth structure. This article describes the treatment of internalized discoloration of dentin under porcelain crowns. (J Prosthet Dent 2009;101:153-157).