The purpose of this study is to explore the pain-reieiving effects and safety of tramadol HCl/acetaminophen as compared to placebo in patients experiencing painful diabetic neuropathy. Treatment of neuropathic pain often requires the use of more than one medication. The pain-relieving potential of tramadol HCl/acetaminophen for the treatment of painful diabetic neuropathy comes from the multiple mechanisms of action in this combination pain medication. Patients who experience painful diabetic neuropathy will be enrolled in this study.