Candidal infection in oral lichen planus. The prevalence of candidal infection in lichen planus (LP) and its possible association with ulceration were independently examined in two archived series of 108 and 77 cases derived from two separate populations. To ensure that similar material was being compared, each case was histopathologically reassessed and confirmed as LP or reclassified as nonspecific lichenoid stomatitis (NSLS), lichenoid dysplasia (LD), or other (O). Three further sections, cut at 25 microns intervals, were stained with periodic acid-Schiff reagent for the identification of intraepithelial candidal pseudohyphae. As control specimens, 61 normal and 59 hyperkeratotic mucosal samples were similarly processed and examined. Candidal infection was found in 17.4% and 16.4% of ulcerated and nonulcerated LP cases, respectively, and in 40.0% and 16.7% of ulcerated and nonulcerated NSLS cases, respectively. One case of LD was infected. Each control series contained one infected case. The results indicate that candidal infection occurs more readily in LP and NSLS, with no apparent association with ulceration in LP. The comparatively marked increase in the infection prevalence of ulcerated NSLS cannot be statistically confirmed, and its significance remains uncertain. 