In this retrospective study, quantitative Sézary cell counts were performed at presentation on 192 patients with erythrodermic cutaneous T-cell lymphoma (E-CTCL). Per recommendation of the International Society of Cutaneous Lymphomas (ISCL), the impact on staging of using an absolute Sézary cell count of 1.0 K microL-1 or more as equivalent to lymph node involvement was investigated. Of 132 patients with disease initially classified at stage III using the current TNM staging system, 25% were up staged to IVa, resulting in a clearer separation of associated survival curves between the stages. Furthermore, the current ISCL definition of B0, B1 and B2 ratings were improved using Sézary cell count levels of < 1.0 K microL-1, > or = 1.0 - 4.99 K microL-1 and > or = 5.0 K microL-1, respectively. These modified B ratings potentially could be used in an alternative staging system for E-CTCL without N rating. Advanced age, prior exposure to multiple systemic drugs, enlargement of peripheral lymph nodes (>3 cm), other measures of blood tumor burden (CD4/CD8 ratio > or = 10, chromosomally-abnormal clone) and 2-fold increase in serum LDH level were other factors of prognostic significance. The clinical importance of these variables vis-à-vis the modified TNBM staging system will need to be clarified in future studies.