Insomnia is a common complaint or disorder throughout the world. About one third of the population in the industrial countries reports difficulty initiating or maintaining sleep, resulting in a non-refreshing or non-restorative sleep. The majority of the insomniacs suffer chronically from their complaints. It has been reported that in patients with chronic insomnia lasting longer than six months, 50% had a past or current mental disorder. This raises the possibility that treatment of insomnia may reduce the risk for psychological conditions. This double-blind, placebo-controlled, parallel, randomized clinical trial is designed to assess the efficacy and safety of esmirtazapine in patients suffering from chronic primary insomnia.