Systemic lupus erythematosus patients who develop hemolytic anemia or thrombocytopenic purpura differ from other lupus patients and are similar enough to be considered two related subsets with a more benign course. Thirty-one lupus patients with either or both these hemocytopenias were found to be significantly younger, more often males, and had less frequent fever, polyarthritis, serositis, cutaneous vasculitis, nephropathy, neurologic manifestations, and persistent hypocomplementemia than 62 lupus patients without any of these hemocytopenias. They also had lower index scores of overall disease severity and required less treatment. It seems important to subdivide lupus patients in subsets for therapeutic and prognostic purposes.