Bartonella quintana is a reemerging pathogen responsible for trench fever, endocarditis, bacteremia, and bacillary angiomatosis. We previously reported the first case of a patient with B. quintana-induced chronic adenomegaly, and here we present a report on a second patient. A hemodialyzed patient with Sjögren's syndrome presented with mediastinal adenomegalies and secondary pancytopenia. All diagnostic investigations remained negative, except that a Bartonella-like microorganism was isolated from a bone marrow biopsy. The isolate was identified as B. quintana by a specific mouse polyclonal antibody and by determination of a partial gltA (citrate synthase-encoding) gene and 16S rRNA gene sequences. DNA of the pathogen was also detected in the adenomegaly and in the serum of the patient by PCR amplification of the gltA gene. Anti-B. quintana antibodies were never detected in the patient's serum throughout the 12-month follow-up but were detected in the serum of the patient's cat. The patient's outcome was favorable after treatment with gentamicin. Chronic adenomegaly in seronegative patients is a new clinical entity due to B. quintana.