AbstractAcute lymphoblastic leukemia was observed in a 22‐year‐old white female patient and was manifested by normal platelet counts, 50–60% hand mirror cells (HMC) in the bone marrow, and prolonged survival without treatment. The characteristic neoplastic cell had a nucleus within the “mirror” portion and a cytoplasmic uropod forming the “handle” portion. The presence of acid phosphatase and B‐glucuronidase activity suggested that the cell was a T cell lymphoblast. However, extensive immunologic surface marker studies indicated the cells were non‐T, non‐B. Terminal transferase activity further supported the lymphoid nature of the cell. The hand mirror cells were considered a real phenomenon since they were demonstrated on phase contrast microscopy, scanning electron microscopy, and transmission electron microscopy. The cells did not grow in tissue culture and cytogenetics revealed a normal female karyotype. From the above observations, the HMC is a lymphoblast with morphological, cytochemical, and immunological features which may differentiate it from the usual cell in acute lymphoblastic leukemia. Therefore, cases involving increased numbers of hand mirror cells in the bone marrow and acute lymphoblastic leukemia require further investigation to elucidate the full importance of this cell. This study represents the first attempt to investigate