In 1923 B. B. Woodward published his "Catalogue of the British species of Pisidium", a work he hoped would stabilise the nomenclature of a poorly understood genus of freshwater bivalves and place its study on a firm footing. Copiously illustrated with photos based on specimens housed in the Natural History Museum, London, and in other collections, the book was studied minutely by three malacologists with considerable experience of British freshwater molluscs, A. W Stelfox, C. Oldham and R. A. Phillips. They proved that Woodward’s book was full of misunderstandings and erroneous identifications. Stelfox, in various publications, took him to task and the two men became engaged in a drawn out and contentious war of words. The ‘Pisidiuim Affair’ ended after Woodward’s death in 1930 and was soon forgotten by all but a few. In 1960 the two authors of this article joined forces and examined the specimens illustrated in the book, intending to publish a revision of Woodward’s identifications. That intention was not realised and now, some 40 years later, would serve no useful purpose. Instead, they have attempted to place Woodward’s pioneering work and the controversy it engendered in a historical perspective. Their analysis of Woodward’s contribution to the study of Pisidium shows that he had an imperfect understanding of the genus, due principally to his lack of field experience. Consequently, they support the views expressed by Woodward’s three principal critics, Stelfox in particular, while at the same time giving due credit to Woodward for his laborious and partially successful attempt to make sense of a notoriously difficult genus of freshwater bivalves.