T-lymphoblastic leukemia/lymphoma (LBL and ALL) is a rare lymphoid malignancy typically presenting in adolescent and young adult males. Patients are traditionally treated with ALL-type protocols, with no consensus on the role of maintenance therapy, or allogeneic or autologous transplant. Outcome results are thus difficult to interpret. The successful use of intensified ALL protocols in patients <25 years with lymphoblastic malignancies without transplant prompted the Haematology Unit at St James's Hospital (SJH) to change practice in 2005 from transplanting in first complete remission (CR1) to treating patients <25 years with chemotherapy alone. We reviewed the outcome of patients treated before 2005 in order to compare the pre- and post-2005 management approaches in the future. This retrospective study included 31 patients with T-LBL treated from 1980 to 2004. The patients were divided into group A (16-25 years) and group B (>25 years). Twenty-one patients had an allograft in CR1 (group A, n = 12 and group B, n = 9). For the allografted patients the 5-year EFS and OS was 57%, with a treatment related mortality of 10%. In conclusion, this series confirms that allograft in CR1 has an acceptable cure rate, and we will use these results to benchmark outcomes using pediatric-type protocols in the future.