Almost 50% of cutaneous B-cell lymphoproliferative infiltrates are derived from follicular center cells. Among these, about 25% show a rapidly progressive course, whereas about 75% account for flattening of the survival curve after about 7 years. This group is referred to as semimalignant ("pseudolymphomatous") cutaneous B-cell lymphoma (SM-CBCL). Clinical, histologic, and phenotypical criteria for their differentiation from B-cell pseudolymphoma and from CBCL have been investigated in 60 patients (11 CBCL, 30 SM-CBCL, 19 PSL). Semimalignant CBCL are different from malignant CBCL because they do not tend to disseminate to extracutaneous sites or to transform into high-grade malignant blast-type lymphomas; follicular center cell formation with CD21 positive dendritic reticulum cells is usually present; and normal survival time is not affected. On the other hand, SM-CBCL differ from PSL in that complete cure of the usually multiple and disseminated skin manifestations is not possible and that follicular center formation and the network of CD21-positive cells in conjunction with a kappa or lambda light chain restriction of cellular surface immunoglobulins is seen. If these and other criteria are taken together, differentiation of these various nosologic entities demanding different therapeutic approaches can be achieved with significant reliability.