 This study will assess the benefits and harms of screening for monoclonal gammopathy of undetermined significance MGUS. The overall and disease-specific mortality will be compared between screened and not screened participants. All individuals registered as inhabitants in Iceland and born in 1975 or earlier have been invited to participate. The hypothesis is that an early detection of multiple myeloma MM, through follow-up of MGUS, will improve overall survival and decrease complications associated with diagnosis and treatment of MM. 