A patient with advancing renal failure attributed to focal segmental glomerulosclerosis was found to have marked NK (CD56+) cell expansion and large granular lymphocytic leukemia. Subsequent living-related renal transplantation was accomplished with two early bouts of acute cellular rejection requiring therapy with methylprednisolone and monoclonal antibody OKT3. Chronic triple drug immunosuppressive therapy has substantially reduced the marked NK (CD56+) proliferation. The renal transplantation remains successful after 15 months despite persistent but reduced numbers of circulating NK cells, the potential role of which in the pathogenesis of the underlying nephropathy or the cellular rejection process remains speculative.