The aim of this post-marketing observational study (PMOS) was to obtain further data on long-term safety, efficacy, and quality of life outcomes for adalimumab in routine clinical use in participants with moderate to severe chronic plaque psoriasis after unsustainable clinical response to other biologic disease modifying anti-rheumatic drugs (BDMARDs). There are few data so far showing the effects of switching from other BDMARDs to adalimumab in patients with moderate to severe chronic plaque psoriasis. This study was designed to evaluate the long-term effectiveness of adalimumab in participants with moderate to severe chronic plaque psoriasis using the Psoriasis Area and Severity Index (PASI) in participants previously treated with efalizumab, infliximab, or etanercept and who either never achieved satisfactory response, achieved satisfactory response initially but lost it over time, or discontinued treatment due to intolerance/side effect(s) or other reasons, for example after regular stop of etanercept.