Amyloid light chain (AL) amyloidosis and multiple myeloma (MM) are both clonal plasma cell disorders, and may be concurrently present in patients. However, symptomatic MM seldom develops in patients with AL amyloidosis, while the other way around is common. With this case report, we discuss the difficulties in the differential diagnosis between AL amyloidosis and MM, and extend on the possible mechanisms involved in the development of these overlapping disorders. In addition, we provide clinicians with tools that may help improve their management and monitoring of such patients.