The subject was a 22-year-old woman who developed high fever and arthralgias and eruptions in the extremities around June 2005. She sought medical advice at a nearby dermatology clinic, where hepatic dysfunction was noted on blood testing. The patient was thus hospitalized the next day. Although CRP levels were significantly high, no sign of infection was observed and bone marrow cell differentiation was normal. Adult onset Still's disease was diagnosed based on the observation of persistent high fever >39 degrees C, eruptions, increased leukocytes, pharyngeal pain, splenomegaly, hepatic dysfunction, negative autoantibody results from blood testing, and high serum ferritin levels. Administration of prednisolone 30 mg/day was initiated, but proved ineffective. Steroid pulse therapy was conducted, and the subject was transferred to our medical facility for continued treatment. Attempts were made to control the disease using combined steroid and cyclosporine administration; but exacerbation of high serum ferritin levels and hepatic dysfunctions were observed, so a second course of steroid pulse therapy was conducted. Symptoms improved temporarily, but steroid levels were difficult to reduce. Cyclosporine was therefore replaced by methotrexate, and administration of infliximab was initiated. In the course of treatment, administration of a sulfamethoxazole/trimethoprim combination was initiated, but was discontinued due to suspicion of drug-induced hepatic injury. A second administration of infliximab was conducted in late August, and rapid improvements in clinical symptoms and abnormal test values was observed. However, high fever and headache developed suddenly in early September. Based on the results of spinal fluid testing, blood and spinal fluid cultures and MRI of the head, Listeria meningoencephalitis was diagnosed. Diplopia and impaired consciousness occurred during the disease course, and formation of a brain abscess was observed on imaging. However, symptoms were controlled by long-term combination administration of ampicillin and gentamicin. Administration of infliximab was discontinued for treatment of adult onset Still's disease, and steroid levels were reduced following double-membrane filtration plasma exchange. On follow-up, no relapse of symptoms or abnormalities in blood test values were observed, so the subject was discharged from our medical facility in December 2005. In treatment for rheumatic diseases, a dramatic improvement in treatment results for pathologies displaying tolerance against conventional treatments has been acquired with the development of biological drugs. However, opportunistic infections represent a serious problem, and appropriate preventative measures are required. The present report describes a case in which the subject was affected by Listeria meningoencephalitis during administration of infliximab for steroid-dependent adult Still's disease. Since listeriosis is one of the complications, along with tuberculosis, that warrants precautionary measures, this case is reported and discussed.