Lack of a systematic assessment of insomnia has led to large variations in its reported prevalence in the general population. This study aims to provide new guidelines to assess insomnia prevalence. A cross-sectional telephone survey using the Sleep-EVAL system was done with 24,600 general population-based subjects 15 years and older representative of general populations (France, the UK, Germany, Italy, Portugal, and Spain) consisting of 251,405,391 inhabitants. The overall participation rate was 81.0%. Within the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV) symptomatology for insomnia, 27.2% (95% confidence interval: 26.6-27.8%) of the sample reported difficulty initiating sleep (DIS) (10.1%) or maintaining sleep (DMS) (disrupted sleep (DS): 18.0%; early morning awakening (EMA): 10.9%) or nonrestorative sleep (NRS) (8.9%) at least three times per week; 48.5% of them were concomitantly suffering of a DSM-IV sleep/mental disorder. A factor analysis identified several variables strongly related to each of the major factors of insomnia allowing: (1) The narrowing of the definition of insomnia: the prevalence of insomnia decreased to 16.8% with 64.5% of insomnia subjects having a DSM-IV sleep/mental disorder; (2) The identification of a sleep-deprived (voluntary or not) group without insomnia symptoms, representing 2.1% (1.9-2.3%) of the sample. Interestingly, the latter group closely matched the definition of insufficient sleep syndrome as described by the International Classification of Sleep Disorders (ICSD). Using more delineated criteria to assess insomnia increases the recognition of subjects complaining about sleep. Classifications should be amended to improve the correct identification of insomnia. Sleep-deprived subjects should also not be neglected.