BACKGROUND: Available data concerning the contribution of patient adverse drug reaction (ADR) reporting in practice are scarce. Few studies have compared patients' reports with reports from healthcare professionals (HCPs). During the 2009-10 mass immunization campaign with A (H1N1)v2009 pandemic influenza vaccines, a reinforced pharmacovigilance plan was introduced in France according to European Medicines Agency recommendations. For the first time, patients were offered the opportunity to report suspected ADRs to pandemic vaccines directly to regional pharmacovigilance centres. OBJECTIVE: The aim of the study was to compare the characteristics of patient and HCP ADR reports in order to assess the qualitative and quantitative contribution of patient reporting to the French Pharmacovigilance System. METHODS: All spontaneous ADRs registered into the French Pharmacovigilance Database from 21 October 2009 to 15 June 2010, in which either one of the most frequently administered pandemic vaccines (i.e. Panenza® or Pandemrix®) was involved, were analysed. ADRs were classified as 'serious', 'medically serious' and 'non-serious'. This study focused on 'serious' and 'medically serious' ADRs. An ADR was ranked as 'medically serious' when it required medical intervention or hospitalization within less than 24 hours. In each level of seriousness, frequency of 'unlabelled' ADRs, ADRs of 'special interest', imputability scores and category of ADRs according to Medical Dictionary for Regulatory Activitives (MedDRA®) primary System Organ Class were compared between patient and professional reports. RESULTS: Among the 4746 reports received during the study period, 1006 (21.2%) originated from patients. HCPs reported significantly more 'medically serious' or 'serious' ADRs than patients (15.1% [565/3740] vs 8.4% [85/1006], respectively; p < 0.001). No difference was found in 'unlabelled, serious' ADRs between patients and HCPs (56.5% [n = 13] vs 56.7% [n = 136], respectively). CONCLUSIONS: In this first French experience of formal patient participation to ADR reporting, patient contribution to the total number of ADRs reached 21.2%. This study revealed no major qualitative difference between patient and HCP reports. ADR profiles reported by patients appeared to be consistent with those from professionals. Further investigations are necessary to assess the intrinsic quality of notification forms coming from non-professional reporters. However, this study is of particular interest in the context of publication of the first governmental decree that will formally integrate patient participation to the current French ADR reporting scheme.