Acute leukaemia of ambiguous lineage (ALAL) is a rare form of leukaemia in which morphologic, cytochemical and immuno-phenotypic features of the proliferating blasts lack sufficient evidence to classify them as myeloid or lymphoid in origin or have characteristics of both myeloid and lymphoid cells. We report a 22-year-old man presenting with clinical features of an acute lymphoblastic leukaemia but blasts in his blood and bone marrow with morphological features of myeloblasts. His immuno-phenotyping by flowcytometry showed antigens specific for both myeloid and B-lymphoid lineages. We highlight the importance of correlating clinical features with cellular morphology when diagnosing acute leukaemias, especially when facilities for flowcytometry are not routinely available.