The activation of oncogenic transcription factors defines distinct molecular subsets of T-cell acute lymphoblastic leukaemia and has prognostic relevance in children. We investigated the prognostic effect of the expression levels of eight oncogenic transcription factors—TLX1 (HOX11), TLX3 (HOX11L2), TAL1, TAL2, LYL1, OLIG2 (BHLHB1), LMO1, and LMO2—in 52 adults with T-cell acute lymphoblastic leukaemia. The leukaemia-specific survival rate for the 16 TLX1-positive patients was 88% (90% CI 73–100%), compared with 56% (42–70%) for all other cases (p=0·019). Only the TLX1 oncogene expression subgroup showed difference in leukaemia-specific survival. Our results suggest that overexpression of TLX1 confers a good outlook for adults with T-cell acute lymphoblastic leukaemia. Furthermore, our findings lead to questions about whether stem-cell transplantation in first remission is necessary for effective treatment of patients in the low-risk subgroup of patients with TLX1 oncogene expression.