© 2020 The diagnosis of T-cell lymphomas is often more challenging than that of B-cell lymphomas and can be difficult even for monospecialised haematopathologists. Their identification involves histomorphological assessment and the recognition of aberrant immunophenotypes but may additionally require polymerase chain reaction (PCR)-based analysis of T-cell receptor (TR) gene rearrangements (clonality analysis). TR gene rearrangements occur naturally during T-cell development, acting as a unique barcode for each cell: in neoplastic proliferations subsets of these barcodes become expanded and can therefore be detected as clonal populations. Here we examine the current role of clonality analysis, discussing limitations and possible future directions which may improve diagnostic efficacy and efficiency. This review will provide helpful insight to histopathology trainees as well as non-specialist consultants who may encounter T-cell lymphomas in their routine diagnostic practice. The article is also suitable for practising haematopathologists as a refresher on theory and an insight into possible future developments.