A typical case of balanitis circumscripta plasmacellularis is described in a 74-year-old man. Electron microscopy revealed a dense infiltrate composed mainly of plasma cells and macrophages; the former showed considerable rough endoplasmic reticulum and phagolysosomes, while the latter contained variable amounts of sideromes. A few mast cells, eosinophils and extravasated erythrocytes were also present. Connective tissue was scarce; no elastic fibres and viral particles were seen.