Comparison of Volinanserin and Lormetazepam in the Treatment of Insomnia Characterized by Sleep Maintenance Difficulties

Inclusion Criteria: * Out-patients with Primary Insomnia according to Diagnostic and Statistical Manual of Mental Disorders (DSM-IV-TR) criteria Exclusion Criteria: * Based on patient's information, the patient has spent less than 6.5 hours or more than 9.0 hours, in bed, each night, over the preceding two weeks * Based on patient's information, the patient complains of less than one hour of wakefulness after sleep onset for at least 3 nights per week over the preceding month * Disturbances of sleep maintenance parameters based on the patient's sleep questionnaire during the run-in period differing from pre-defined criteria. * Pregnant or breastfeeding women and women of childbearing potential without effective contraceptive method of birth control * Night shift workers and individuals who nap 3 or more times per week * Consumption of xanthine-containing beverages (i.e., tea, coffee or cola) that comprises more than 5 cups or glasses per day The above information is not intended to contain all considerations relevant to a patient's potential participation in a clinical trial.