Lupoid thrombocytopenia is herein defined as a disorder in which patients with thrombocytopenia have a positive Hep 2 antinuclear antibody. Although these patients may have other clinical or laboratory findings consistent with systemic lupus erythematosus, they do not satisfy the revised diagnostic criteria set down by the American Rheumatism Association (1982). In all other respects they have similar findings to patients with idiopathic thrombocytopenic purpura. Six patients are described with their clinical and laboratory features. It is proposed that this disorder should be distinguished from other forms of autoimmune thrombocytopenia including that associated with systemic lupus erythematosus.