The purpose of this study is to assess efficacy and safety of volinanserin in the population of patients complaining of sleep maintenance insomnia. The patients suffering from that condition frequently wake up during the night, their sleep is non restorative and they suffer from a significant distress or impairment in their daily activities consecutive to insomnia.

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.