Generalized (diffuse) plane xanthoma (GPX) is a normolipaemic xanthomatosis that is very frequently associated with a haematological disorder, and especially with monoclonal gammapathies, which it may precede by several months or years. Here, we report a case of GPX associated with idiopathic Bence-Jones proteinuria, a very rare type of monoclonal gammopathy of undetermined significance. To our knowledge, this association has not been previously described.