The CCAAT/enhancer binding protein a is an essential transcription factor for granulocytic differentiation. Recent studies reported N-and C-terminal CEBPA mutations in approximately 7% of acute myeloid leukaemia (AML) patients. C-terminal mutations are usually in-frame and occur in the basic-leucine zipper (bZIP) domain, resulting in deficient DNA binding. Using a rapid PCR approach, we screened for bZIP mutations and determined the prognostic value of these mutations in a cohort of 277 de novo AMLs. In addition, we set out to quantify CEBPA mRNA levels by ‘real-time’PCR using TaqMan® technology. In-frame insertions were observed in 12 (4.3%) cases. All cases with mutations carried an intermediate-risk karyotype and all but one belonged to M1 or M2 FAB class. Further sequence analysis revealed that CEBPA C-terminal mutations are associated with frameshift mutations in the N-terminus of CEBPA. These two mutations were always found in different alleles. Event-free survival (EFS) and overall survival (OS) of patients with CEBPA mutations were significantly increased (P ¼ 0.02 and 0.03, respectively) in comparison to the patients lacking these mutations. Mutations were associated with a significantly reduced hazard ratio for death (OS: HR ¼ 0.35, P ¼ 0.04) and failure (EFS: no CR, death in CR or relapse, HR ¼ 0.37, P ¼ 0.03). This favourable hazard ratio was maintained after adjustment for cytogenetic risk, FLT3-ITD and CEBPA expression levels in multivariable analysis. In contrast, low CEBPA expression in AML with intermediate-risk karyotype (n ¼ 6) seemed to be associated with poor prognosis (not significant). By including this newly developed PCR assay, we define a subgroup of good-risk patients within the heterogeneous intermediate-risk group of AML. The Hematology Journal (2003) 4, 31–40. doi: 10.1038/sj. thj. 6200216