Siderosis of the lung is generally assumed to be a benign condition, not associated with respiratory symptoms. A review of the literature suggests that this assumption may be incorrect, and that siderosis may lead both to symptomatic and functional changes. It is known that iron ore miners have a raised lung cancer mortality, but this has been attributed to smoking, or exposure to tars or radon. Mortality studies among iron workers (haematite miners, welders, iron foundry and steel workers) show, however, that an association exists between working with iron and death, both from lung cancer and other respiratory causes. A number of surveys have examined respiratory function and symptoms among welders. These indicate that welding is associated with obstructive airways disease. The effect of the welding fume on respiratory function and symptoms can be as great as that of smoking. Iron has also been shown to cause fibrosis in some cases. Small functional changes of restriction and loss of lung compliance are often due to iron alone. The fibrosis may be enhanced by associated silica exposure. A number of constituents of welding fume could, along with iron, contribute to pulmonary changes. The presence of siderosis may act as a good marker of exposure to fume and any resulting disability.