We report the case of a patient with amyloid light-chain (AL) amyloidosis, presenting for more than 1.5 years with oligoarthritis as the only clinical symptom of the underlying disease. Developing further organ symptoms (heart and gastrointestinal tract) led to the definitive diagnosis. Joint involvement due to AL amyloidosis is extremely rare and may mimic rheumatoid arthritis. Arthritis might be the first symptom of the AL amyloidosis. The combination of arthritis and other organ disorders (e.g., proteinuria, heart failure, or diarrhea) should initiate further diagnostic efforts considering AL amyloidosis as a differential diagnosis. The diagnosis will be confirmed by the typical histology of synovia or involved organs including immunohistochemistry for typing amyloid and performing immunoelectrophoresis.