One of the problems with immunohistochemistry is that storage of unstained slides can have a detectable negative effect on the intensity of staining for various antigens. This has not been well studied for the p63 antigen. A time-course study was performed to evaluate the effect of storage on the intensity of p63 immunohistochemical staining. Slides from various breast lesions/foci were stained with a p63 antibody on day 0 and after storage at room temperature for 2, 4, and 8 weeks. A p63 intensity score, ranging from 0 to 300, was calculated using the intensity (0, 1, 2, or 3+) and percentage of peripheral myoepithelial cell staining (0% to 100%). There was a progressive decline in the p63 intensity score with time with the differences between day 0 and 2 weeks and 2 and 4 weeks being statistically significant (P=0.037 and 0.001, respectively), whereas that between 4 and 8 weeks was not (P=0.075). These findings confirm a time-dependent decline in p63 immunostaining intensity evident as early as with 2 weeks of storage and still present after 8 weeks. This should be considered in the evaluation of p63 immunostains performed on stored unstained sections, both in diagnostic surgical pathology and in translational research studies.