All these criteria must be present:

• Biopsy proof of a plasma cell tumour
• No lytic bone lesions except the tumour itself
• Bone marrow plasma cell proportion less than 10%
• For solitary plasmacytoma of bone: no significant PET scan or CT scan abnormality at another site

A serum and/or urine monoclonal paraprotein may be present. Usually the uninvolved immunoglobulin levels are normal.​​