The primary objective is to compare the potential for next-day residual effects of eplivanserin 5 mg/day and lormetazepam 1 mg/day by measuring the sleepiness in the morning using the patient's sleep questionnaire during 4 weeks of treatment in patients with chronic primary insomnia and sleep maintenance difficulties.

The secondary objectives are to compare the clinical safety of both products, including the potential for rebound insomnia and withdrawal symptoms after treatment discontinuation, to compare the efficacy of both products on subjective sleep parameters and to compare the effects of both products on patient's daytime functioning.

Inclusion Criteria:

• Primary Insomnia according to Diagnostic and Statistical Manual of Mental Disorders (DSM-IV-TR) criteria
• At least 1 hour of wakefulness for at least 3 nights per week during the month preceding inclusion
• Disturbances of sleep maintenance criteria based on the patient's sleep questionnaire during the run-in period

Exclusion 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
• Insomnia secondary to a general medical condition

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