Panic disorder (PD) is one of the most common psychiatric disorders. Web-based self-help treatments for PD have had promising results. These online treatments seem to have larger effect sizes (ESs) when professional support is added. However, the amount of support or how it should be administered is not yet clear. The aim of this trial was to study two ways of administering psychological support provided by phone as a part of Internet-based self-help treatment for PD based on cognitive behavioral therapy. Please contact the library to receive a copy of this article - http://bit.ly/1Xyazai