This phase 3 trial is being conducted at approximately 80 sites in the United States (U.S.) to investigate whether lacosamide (SPM 927) at different doses reduces pain in subjects with diabetic neuropathy. Approximately 455 subjects will be randomized to placebo or to one of three doses of lacosamide. To qualify for this trial, subjects with symptoms of painful distal diabetic neuropathy ranging in duration from 6 months to 5 years must have an average pain intensity of greater than or equal to 4 on an 11-point Likert scale (0-10 scale) during the 7 day period prior to the start of treatment.

To determine what effect lacosamide has on diabetic neuropathic pain, subjects will use a diary to record their daily pain intensity (morning and evening; and pain interference with sleep (morning) and activity (evening). Use of rescue medication (acetaminophen) and subjects' quality of life will be investigated. In addition, the safety and tolerability of the different doses of lacosamide will be investigated.

Inclusion Criteria:

• Diabetic neuropathy

Exclusion Criteria:

• Subject has previously participated in this trial or subject has previously been assigned to treatment in a trial of the drug under investigation in this trial.