The cutaneous T-cell lymphomas (CTCLs) comprise a spectrum of non-Hodgkin lymphomas with a predilection for the skin. This heterogeneous group of CTCLs include the prototypic CTCL mycosis fungoides (MF) and the recently described Ki-1+ lymphomas. MF is notoriously difficult to diagnose in its early stages. The histologic appearance of early MF is indistinguishable from that of chronic dermatitis. The limitations of light microscopy in the diagnosis of the CTCLs have led to the development of other diagnostic laboratory techniques. The best approach to the diagnosis of the CTCLs is a multidisciplinary one and should include ultrastructural morphometry, immunophenotyping, immunogenotyping, and histologic evaluation whenever possible. It is the purpose of this overview to point out the strengths and weaknesses of each of these techniques and, together with clinical input, to provide a comprehensive and rational approach to patient care.