Several of the methods of treating plaque-stage mycosis fungoides (MF) advocate treatment of the whole skin, although relatively little information exists on the histologic appearance of clinically uninvolved MF skin. Our study was performed to elucidate the histologic appearance of the clinically uninvolved skin of plaque-stage MF patients. Biopsies were taken from the clinically uninvolved skin of 18 untreated patients with plaque-stage MF, 1 cm (near) and ≥10 cm (far) from the MF plaques, and from 23 normal, healthy controls. Eight to 12 serial sections from each specimen were examined. The most common histologic finding, which was observed in six (33%) biopsies of near skin and four (22%) biopsies of far skin compared with only one (4%) biopsy of normal control (p = 0.02 and 0.1, respectively), consisted of mononuclear-cell infiltrate around a blood vessel in the papillary dermis, with extension of some of these cells into the overlying epidermis. More diffuse and epidermotropic mononuclear cell infiltrates were seen in an additional three (17%) biopsies of near skin, whereas mild nonepidermotropic superficial perivascular or perifollicular mononuclear cell infiltrates were observed in an additional four (17%) biopsies of the normal controls. In conclusion, the most common histologic finding in our study, which was observed predominantly in the MF group, might represent an earlier stage and clinically undetectable involvement of the normal-looking skin in MF patients.