History of any sleep disorder, or any Diagnostic and Statistical Manual of Mental Disorders IV (DSM-IV) axis I disorder other than primary insomnia.

Sleep apnea, or restless legs syndrome.

Daytime napping of more than 1 hour per day.

Important caffeine consumption, heavy tobacco use, alcohol or drug abuse within 2 years prior to the screening visit.

Unwillingness to refrain from drugs, over-the-counter or herbal medication having an effect on sleep or behavior.

Almorexant (ACT-078573) in Elderly Subjects With Chronic Primary Insomnia