6 showed the CD10 expression in childhood B lineage ALL is associated with several favorable presenting features but is not an independent prognostic factor [13, 28–30]. In T cell lineage, the expression of CD10 was independently associated with favorable clinical outcome [14, 23]. However, for the larger subgroup of patients with T-lineage ALL, CD10 expression has no independent prognostic signiﬁcance [30]. Aberrant expression of myeloid antigens (MyAgs) on acute lymphoblastic leukemia cells is a well-documented phenomenon and has no prognostic or therapeutic implica- tions [15, 31–33] but can be used for monitoring MRD [32]. The myeloid-associated antigens CD13/CD33 used in the current study were the most commonly expressed in children ALL cases, and their incidence should be representative of overall MyAgs expression [15]. In the present study, MyAgs expression occurs in 52.7% of all cases (57.4% of pB cell ALL and 33.9% of T-ALL). This frequency is higher than in previous studies (between 6% and 35%) [15, 28, 31, 33]; however it is comparable to those reported by Khalidi et al. [21]. The diﬀerences observed are probably due to the criteria used to deﬁne a “percent positive” cell and the number of antigens tested [15, 21]. We can draw the following conclusions from our study: (1) we conﬁrm the excellent practicability of the two immunophenotyping steps strategy for classiﬁcation of ALLs, especially in countries with limited resources; (2) the distribution of ALLs in Moroccan children is similar with the general distribution pattern in developed countries, except for the high frequency of T-ALL phenotype; (3) the phenotypic proﬁle of our patients is close to those reported in literature for B-lineage ALLs. For the T-cell ALL subgroup, the blast cells express more CD1a, surface CD3, and CD4 while expressing less TdT. The high frequency of CD1a expression resulted in an excess of the common thymocyte subtype. 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