Pagetoid reticulosis (PaRet) is a rare skin disease with an intraepidermal infiltrate of atypical lymphocytes. We performed phenotypic studies on two patients with classic localized PaRet (Woringer-Kolopp disease) and one patient with the disseminated type (Ketron-Goodman disease) and compared these with all published reports of cases; both variants show intraepidermal, highly activated, proliferating T cells with variable loss of pan-T-cell antigens, contrasting with nonactivated dermal reactive T cells. This pattern is unique among cutaneous lymphomas and can be used for diagnosis. Despite the fact that localized PaRet does not show a malignant course, recent genotypic analysis of one patient showed monoclonality. Comparable constellations are found in other diseases like lymphomatoid papulosis, which also represent monoclonal disorders of activated T cells with a benign course. To unify these seeming discrepancies, we introduce the concept of "benign cutaneous lymphomas."