Interferon-α (IFN-α) therapy is commonly used in the treatment of neoplastic and autoimmune diseases, including cutaneous T cell lymphoma (CTCL). However, the IFN-α response is unpredictable, and the IFN-α cell targets and pathways are only partially understood. To delineate the molecular mechanisms of IFN-α activity, gene expression profiling was performed in a time-course experiment of both IFN-α sensitive and IFN-α-resistant variants of a CTCL cell line. These experiments revealed that IFN-α is responsible for the regulation of hundreds of genes in both variants and predominantly involves genes implicated in signal transduction, cell cycle control, apoptosis, and transcription regulation. Specifically, the IFN-α response of tumoral T cells is due to a combination of induction of apoptosis in which TNFSF10 and HSXIAPAF1 may play an important role and cell cycle arrest achieved by downregulation of CDK4 and CCNG2 and upregulation of CDKN2C and tumor suppressor genes (TSGs). Resistance to IFN-α appears to be associated with failure to induce IRF1 and IRF7 and deregulation of the apoptotic signals of HSXIAPAF1, TRADD, BAD, and BNIP3. Additionally, cell cycle progression is heralded by upregulation of CDC25A and CDC42. A critical role of NF-κB in promoting cell survival in IFN-α-resistant cells is indicated by the upregulation of RELB and LTB.