Cytogenetic analysis of a granulocytic sarcoma in a patient without systemic leukaemia. Granulocytic sarcoma is a rare complication of leukaemia. Occasionally it presents before the development of systemic leukaemia when diagnosis may be difficult. A case of granulocytic sarcoma occurring in a patient with no overt evidence of leukaemia, but in whom cytogenetic analysis of the bone marrow showed a clonal t(12;13) translocation, is reported. Cytogenetic analysis of tissues in this disease may indicate evidence of systemic disease before overt morphological changes. 