 All individuals that are registered as inhabitants in Iceland and born in 1975 or earlier have been invited to participate in the study. After signing informed consent, serum from the participants will be analysed for MGUS. The participants will not be contacted for blood sampling. Instead, an innovative approach will be used by taking advantage of the fact that most people 40 years or older do a blood test for various reasons during a three year period. The ID-list of participants in the study will be cross-linked with all major laboratories in Iceland, covering approximately 90 of all blood sampling in Iceland. When a participant has a blood test, a small amount 1 ml of serum will be sampled and put in a separate test tube belonging to the study and used for diagnosis of MGUS. 