First we performed a literature search for articles on pneumonitis as a side-effect of HCV treatment in order to obtain a comprehensive overview of this particular side-effect. We took advantage of the PubMed and Web of Science interface (http://www.ncbi.nlm.entrez and http://apps.isiknowledge. com) and searched with the following keywords: interferon, interstitial, pneumonitis, and hepatitis C, for the period 1990-2008. Articles written in English, French or German were included in the analysis. Furthermore, we searched the three drug toxicity databases. We included the Netherlands Pharmacovigilance Center (www.lareb.nl) database and the Fig. 1 a Chest X-ray with diffuse, bilateral interstitial pattern. b High-resolution computer tomography image showing bilateral ground-glass opacities in central zone Drug-Induced Lung Diseases database (www.pneumotox. com), and lastly we performed an exhaustive search of the database of the World Health Organization (WHO) via the Uppsala monitoring center (http://www.who-umc.org). We used as keywords interferon and pneumonitis. The WHO database is a collection of data about adverse drug reactions from around the world, especially from countries that are members of the WHO, and the generation of signals of drugs which might possibly have problematic side-effects.