The objective of this study was to identify the causes of under-reporting of adverse drug events in hospitals in Cameroon. From a strategic point of view, we focused our work on three points: firstly, the evaluation of the knowledge of health professionals in pharmacovigilance; this study revealed an insufficient level of knowledge in pharmacovigilance among the categories of health professionals. Then the determination of their attitudes towards the manifestations of adverse drug events; it emerged that health professionals had a positive attitude towards ADRs in hospitals, that the proportion of adverse events varied according to the type of hospital and that the level of notification was the same in all reference levels. Finally, the factors that hinder the functioning of pharmacovigilance in hospitals were identified.