A patient presented with a heavily pigmented ciliary body tumour accompanied by diffuse pigmentation of the iris and chamber angle and secondary open angle glaucoma. The case was diagnosed clinically as malignant melanoma and melanomalytic glaucoma, and the eye was enucleated. Routine histopathology, immunohistochemistry, and ultrastructural studies revealed the tumour as being of the spindle cell type with extensive necrosis accompanied by a massive macrophagic response. The iridocorneal angle was heavily infiltrated by large pigmented cells, which were identified as being predominantly melanomacrophages. This is consistent with the few previous descriptions of this condition and confirms the view that the aqueous outflow obstruction is simply a mechanical process. Most of the native trabecular endothelial cells, which had also phagocytosed large quantities of melanin, still maintained their normal relationship to the trabeculae, though there were signs of activation. Immunohistochemistry and electron microscopy revealed the presence of moderate numbers of tumour cells on the iris surface and in the trabecular meshwork distant from the primary tumour site. The importance of these findings to the management of anterior uveal melanomas with secondary open angle glaucoma is discussed.