Scleromyxedema or generalized diffuse lichen myxoedematosus is a rare mucinosis that is associated with monoclonal gammopathy and which frequently affects multiple extracutaneous organ systems. The pathogenesis of scleromyxedema has not been fully elucidated, but includes stimulation of glycosaminoglycan synthesis. The clinical course of scleromyxedema is chronic and often progressive, leading to severe morbidity and even death. The characteristic skin findings encompass multiple waxy papules often on indurated plaques, while thickening of skin leads to conspicuous folds on glabella and dorsal aspects of finger joints. Microscopical manifestations are dermal deposits of glycosaminoglycans between collagen bundles in reticular dermis, increased numbers of fibroblasts and fibrosis as well as loss of elastic fibers. Progressive skin involvement results in decreased mobility of the mouth and joints and even contractures. Extracutaneous manifestations occur in the musculoskeletal or cardiovascular system, in the gastrointestinal or respiratory tract, in the kidneys or in the central and peripheral nervous system. There are no in-label or evidence-based treatments available for scleromyxedema, but by expert consensus high-dose immunoglobulins are considered as treatment of choice, followed in case of insufficient efficacy by systemic glucocorticosteroids and then lenalidomide or thalidomide. In severe and refractory cases, autologous hematopoietic stem cell transplantation has been performed. Long-term maintenance treatment is usually required to prevent recurrences. Close interdisciplinary follow-up is recommended.