The purpose of this study is to explore the pain-relieving effects and safety of Tramadol HCl/acetaminophen as compared to placebo in patients experiencing acute low back pain. Tramadol HCl/acetaminophen is approved for short-term management of acute pain. The combination of tramadol HCl/acetaminophen has been shown to be effective for the treatment of acute musculoskeletal pain. Patients who experienced at least moderate acute low back pain for 2 to 10 days before study entry will be randomized to receive either tramadol HCl/acetaminophen or placebo.