Background: Data on the relative frequency of the various forms of primary cutaneous lymphomas (PCLs) are largely limited to European institutions. Objective: Our purpose was to document the relative frequencies of various PCLs seen at 3 US institutions with active cutaneous lymphoma programs and to compare those with the European data. Methods: Included in this study are newly registered patients seen at MCP Hahnemann University, New York University, and the University of California, San Francisco from July 1, 1995 to June 30, 1998. Results: A total of 755 patients were seen. The frequency distribution of the major diagnostic groups was as follows: mycosis fungoides/Sézary syndrome, 82.3%; lymphomatoid papulosis, 12.6% (including patients with associated mycosis fungoides/Sézary syndrome); CD30⁺ anaplastic large-cell lymphoma, 0.9%; peripheral T-cell lymphomas, 2.9%; B-cell lymphoma, 4.5%. Conclusion: The most striking finding is the much lower relative frequency of primary cutaneous B-cell lymphomas at US institutions (4.5%) versus the approximately 20% reported by European groups. The reason for this difference requires further study. (J Am Acad Dermatol 2000;43:793-6.)