Peripheral T-cell lymphomas (PTCLs) are a biologically diverse and uncommon group of diseases. Compared to their B-cell counterparts, PTCLs remain largely unexplored and the optimal treatment ill-defined due to disease rarity and biological heterogeneity. With the notable exception of ALK-pos anaplastic large cell lymphoma (ALCL), the prognosis of most PTCL subtypes is extremely is poor with a 5 y overall survival of approximately 15-30% in most series. The international prognostic index has been useful in defining different risk groups within some PTCL subtypes, including PTCL unspecified (PTCLU). Attempts have been made to define disease subgroups within the biologically heterogeneous PTCLU based on T-helper chemokine receptor profile and/or gene expression profiling which may aid in tailoring new therapies. Future clinical trials are needed that focus specifically on PTCL to advance our understanding and define the optimal management in this disease.