We here present an extremely rare case of granular lymphocytic leukemia derived from gamma delta T-cell (gamma delta T-GLL). The blood picture at diagnosis was as follows; white cell count 25.7 x 10(9)/l containing 94% atypical lymphocytes with cytoplasmic granules, hemoglobin 11.8 g/dl and platelet count 124 x 10(9)/l. The atypical lymphocytes were positive for CD2, CD3, CD5, CD7, CD56 and TCR gamma delta, but negative for CD4, CD8, CD57, TCR alpha beta and B-cell antigens. The cytotoxic molecules, T-cell intracellular antigen-1 (TIA-1) and granzyme B, were positive by immunocytochemical analysis. Southern blot analysis showed rearrangement of T-cell receptor J gamma and C beta genes but germline configuration of the JH gene. Neither serum antibody against human T-cell leukemia virus type-I (HTLV-I) nor the integration of HTLV-I proviral DNA was detected. CT scan showed splenomegaly but no lymph node enlargement. A diagnosis of gamma delta T-GLL was made, and she has been followed up without any therapies for more than 4 years.