A 60-year-old part Aboriginal woman was observed to develop severe neutropenia and a large granular lymphocyte (LGL) proliferation five years after the diagnosis of systemic lupus erythematosus (SLE). Monoclonality of the CD3+, CD4-, CD8+ LGL population was confirmed using the novel approach of X-linked restriction fragment length polymorphism (RFLP) analysis. Indeterminate HTLV-I serology was present. The patient responded to steroid therapy. LGL proliferation in the setting of SLE and the use of X-linked RFLP analysis to define LGL clonality have not previously been reported.