Waldenstrom's macroglobulinaemia is a malignant disease of B cells which are lymphoplasmacytoid in appearance. These cells secrete IgM paraprotein which gives rise to clinical manifestations.

The disease is commonly seen in elderly men. It is an indolent disease with a median survival of 3 to 5 years, but some patients may survive 10 years or longer. It is regarded as a low grade non-Hodgkin's lymphoma.