We retrospectively studied the immunophenotype by flow cytometry of 20 anaplastic large cell lymphomas (ALCLs) (9 anaplastic lymphoma kinase [ALK]+ and 11 ALK-) with a particular emphasis on the aberrant expression of the myeloid associated antigens CD13 and/or CD33. All ALCLs expressed CD45, HLA-DR, and CD30. Most (8/9) ALK+ ALCLs expressed at least 1 surface T-cell antigen (CD4, 6/9 [67%]; CD7, 6/9 [67%]; CD2, 5/9 [56%]; CD5, 2/9 [22%]; CD8, 2/9 [22%]; CD3, 1/9 [11%]). All ALK-ALCLs expressed at least 1 surface T-cell antigen (CD3, 7/11 [64%]; CD4, 6/11 [55%]; CD2, 6/11 [55%]; CD7, 2/11 [18%]; CD5, 1/11 [9%]; CD8, 1/11 [9%]). CD13 and/or CD33 were expressed in all (9/9) ALK+ ALCLs compared with 1 of 11 ALK-ALCLs (9%) (P < .0001). Surface CD3 was more likely expressed in ALK-ALCLs (7/11) compared with ALK+ ALCLs (1/9) (P .03). The myeloid-associated antigens CD13 and/or CD33 are sensitive but not entirely specific markers of ALK+ ALCLs and should not be misinterpreted as indicating myeloid sarcoma.