To understand the mechanism behind aberrant Akt activation in T-ALL, PIK3CA, PTEN and SHIP1 expression and genotype were assessed. No cell lines or primary ALLs harbored PIK3CA mutations. PTEN was expressed in just one-third of the cell lines, but in two-thirds of the primary ALLs, though in the inactivated (phosphorylated) form. SHIP1 was undetectable in most primary ALL and in the T-ALL cell line Jurkat, which harbored a bi-allelic null mutation and a frame-shift deletion; primary ALL harbored the frame-shift as well as other translationally-inactivating deletions and insertions. The inactivation of SHIP1 could play a central role in the deregulation of Akt pathway and tumorigenesis, perhaps in conjunction with PTEN inactivation.