The natural history of benign monoclonal gammapathy (BMG) has been followed by repeated studies of patients with M components through periods up to two decades. The disappearance of an M component is quite exceptional--in this material only once. Populations with increase in IgG, IgA and IgM have been studied separately. Slow, but steady, increase through many years may be found without development of myeloma (MM). Rapid transition from a steady state of the M component to progression is rare and usually, but not always, indicates the development of clearcut myeloma. Intermediate patterns are not uncommon and make it very difficult in rare individual cases to draw a sharp line between myeloma that should be treated and the benign state that should only be observed. The cause of pain may be difficult to judge. Osteolytic foci in the skull are usually diagnostic for MM, but vertebral fracture may also occur in osteopenia. It is evident that a period of at least three years of close observation without treatment should be the routine. "Prophylactic" treatment of BMG with cytostatic drugs should never be attempted.