Inclusion Criteria:

• Diagnosis of primary insomnia based on Diagnostic and Statistical Manual of Mental Disorders (Fourth Edition) criteria
• Disturbances of sleep maintenance criteria based on patient's information related to sleep pattern during the preceding month
• Specific criteria based on the NPSG recordings during the screening nights

Exclusion Criteria:

• Females who are lactating or who are pregnant
• Night shift workers, and individuals who nap 3 or more times per week over the preceding month
• Consumption of xanthine-containing beverages (i.e. tea, coffee, cola) comprising more than 5 cups/day
• Participation in another trial having received study medication within 1 month before the screening visit
• Body Mass Index ≥ 33
• Use of over-the-counter medications such as tryptophan, valerian root, kava, melatonin, St. John's Wort, Alluna or prescription sleep medication
• Use of any substance with psychotropic effects or properties know to affect sleep/wake
• History of primary hypersomnia, narcolepsy, breathing-related sleep disorder, circadian rhythm sleep disorder, parasomnia, dyssomnia
• Clinically significant, severe or unstable, acute or chronically progressive medical or surgical disorder
• Positive qualitative urine drug screen (opiates, cocaine, amphetamine…)

The above information is not intended to contain all considerations relevant to a patient's potential participation in a clinical trial.