Trimeprazine (TPZ) has been marketed in France since 1959, as tablets and solution containing respectively 5 mg and 40 mg/ml. TPZ is a phenothiazine derivative with known antihistaminic and sedative effects. The first approved indication for TPZ is in the treatment of allergy. However, its frequent sedative effects are undesirable in this indication. The second approved indication is in the treatment of insomnia (5-20 mg/day) and TPZ is an alternative to conventional hypnotics as diazepam, flunitrazepam, zolpidem, butobarbital... Due to the prescription frequency of this medicine in our hospital, we analyzed the naturalistic prescriptions mode and the clinical end point in patients hospitalized for mental illness. On the one hand, using the hospital prescription software, we analyzed: prescriptions frequency, dose regimen and drug associations with hypnotics, anxiolytics and sedative antipsychotics. On the other hand, we came into contact with physicians in order to know their opinion on TPZ and the whole point of that indication. The results showed a very high prescription frequency (139/400 patients; 35%), a marked increase in dose compared to those approved by the French Drug Administration (5-20 mg/day: 5%; 20-200 mg/day: 95%) and main drug association with hypnotics, tranquilizers or antipsychotics, respectively 38%, 65% and 91%. Clinical end points are: non addictive properties and an easily adequation of posology for the drinkable drop form in contrast with tablets. Thus, TPZ appears as a first-line hypnotic in spite of its adverse effects common to phenothiazine (atropinic and antidopaminergic effects) and is a usefull medicine for the treatment of insomnia in psychotic patients.