Lumbar spinal arachnoiditis occurring after diagnostic lumbar puncture is a very rare condition. Arachnoiditis may also present with fever and elevated infection markers and may mimic epidural abscess, which is one of the well known infectious complications of lumbar puncture. We report the case of a 56-year-old man with lumbar spinal arachnoiditis occurring after diagnostic lumbar puncture who was operated on under a misdiagnosis of epidural abscess. In the intraoperative and postoperative microbiological and histopathological examination, no epidural abscess was detected. To our knowledge, this is the first case of a patient with postlumbar puncture arachnoiditis operated on under a misdiagnosis of epidural abscess reported in the literature. The authors suggest that arachnoiditis may mimic epidural abscess due to its clinical and radiological features and should be considered in the differential diagnosis of complications of lumbar puncture.