Background:The frequency of antidepressant (ADs) prescription is high, with general practitioners (GPs)responsible for about 80% of the prescriptions. Some studies considered prescriptions meet DSM criteria, whileothers stress inadequate use. The importance of biological and psychosocial determinants of GP prescriptionbehaviour remains little explored. We aimed to describe the importance of these biological and psychosocialdeterminants and their weight in the daily practice of GPs’.Methods:During a week chosen at random, 28 GPs collected the AD prescriptions made within the previous sixmonths, regardless of the reason for the patient contact. Bio psychosocial and AD treatment characteristics wererecorded for all patients. In a random sample of 50 patients, patient characteristics were assessed via a structuredface-to-face interview with the GP.Results:The frequency of AD prescription was 8.90% [3.94 -17.02]. The GPs initiated 65.6% [60.1-70.8] of theprescriptions. The rate of AD prescription for non-psychiatric conditions was 18%. Patients had from 1 to 9 conditions,showing a high level of multi-morbidity. There was a strong influence of past medical history and contextual problems,such as work related problems.Conclusion:AD prescription is related to complex contextualsituations and multi-morbid patients. GPs use abio psycho social approach, rather than a purely biological assessment. Awareness of these influences could improveprescription by GPs.