A multicentre post-marketing surveillance study was conducted in Switzerland in routine practice and involved 1972 insomniac patients treated with zolpidem, an imidazopyridine hypnotic agent. The patients were representative of the general insomniac population (65% women; mean age 55 years; 29% over 65). Of the patients, 87% were treated with a zolpidem dosage of 10 mg/day and the median treatment duration was 30 days. All adverse events were collected through spontaneous reporting. A total of 175 patients (8.9%) reported 343 adverse events, and 102 (5.2%) of them discontinued treatment. CNS (central nervous system)-related adverse events accounted for 66% of the total, the most common events being residual daytime sedation and insufficient efficacy in 3.7% and 1.6%, respectively; confusion, disorientation, nervousness, nightmares, amnesia, impaired concentration and anxiety were observed in a lower proportion. Gastro-intestinal symptoms, headache and skin reactions were the most frequent non-CNS related effects. No serious adverse event was reported and no new risk factors or at-risk populations were identified. The safety profile of zolpidem is thus consistent with its known pharmacological properties, the results of previous clinical trials, and the cumulative international experience gained with this short-acting hypnotic drug.