In this review we systematically assess our current knowledge about psychogenic non-epileptic seizures (PNES), epidemiology, etiology, with an emphasis on the diagnostic issues. Relevant studies were identified by searching the electronic databases. Case reports were not considered. Articles were included when published after 1980 up till 2005 (26 years). A total of 84 papers were identified; 60 of which were actual studies. Most studies have serious methodological limitations. An open non-randomized design, comparing patients with PNES to patients with epilepsy is the dominant design. The incidence of PNES in the general population is low. However, a relatively high prevalence is seen in patients referred to epilepsy centres (15-30%). Caution is needed in the clinical interpretation of ictal features suggested to be pathognomic for PNES. Video-EEG is widely considered to be the gold standard for diagnosing PNES. Still the differential diagnosis epileptic/non-epileptic seizures can be difficult. Despite the current available technical facilities, the mean latency between onset of PNES and final diagnosis as being non-epileptic and psychogenic is approximately 7 years. One of the reasons for diagnostic delay is that the diagnosis of PNES is often limited to a 'negative' process and consequently PNES is characterized as a 'non-disease' (i.e. 'not epilepsy'). The psychological diagnosis is thus an important, although not a conclusive, 'second phase' aspect of medical decision making. Specific relations between seizure presentation and underlying psychological mechanisms are not conclusive. A classification between major motor manifestations and unresponsiveness is recognized. With respect to psychological etiology, a heterogeneous set of factors have been identified that may be involved in the causation, development and provocation of PNES.