Many systemic diseases have cutaneous manifestations. In some diseases skin involvement is the predominant factor (Behçet's syndrome, urticaria pigmentosa, discoid lupus erythematosus and pseudoxanthoma elasticum); in others the skin manifestations, when present, are an important part of the condition (sarcoidosis, systemic lupus erythematosus, hypersensitivity angiitis, porphyria). This report includes descriptions of and comments on these cutaneous manifestations. Erythema nodosum and erythema multiforme are reaction patterns of the skin and mucous membrane which may have many causes. The relationship between discoid and systemic lupus erythematosus is discussed. There is little doubt that these are variations of the same basic disease process, even though the prognoses are very different.