The worldwide Incidence and Prevalence of Psoriasis is poorly understood. To better understand this, we performed a Systematic Review of published population-based studies on the Incidence and Prevalence of Psoriasis. Three electronic databases were searched from their inception dates to July 2011. A total of 385 papers were critically appraised; 53 studies reported on the Prevalence and Incidence of Psoriasis in the general population. The Prevalence in children ranged from 0% (Taiwan) to 2.1% (Italy), and in adults it varied from 0.91% (United States) to 8.5% (Norway). In children, the Incidence estimate reported (United States) was 40.8/100,000 person-years. In adults, it varied from 78.9/100,000 person-years (United States) to 230/100,000 person-years (Italy). The data indicated that the occurrence of Psoriasis varied according to age and geographic region, being more frequent in countries more distant from the equator. Prevalence estimates also varied in relation to demographic characteristics in that studies confined to adults reported higher estimates of Psoriasis compared with those involving all age groups. Studies on the Prevalence and Incidence of Psoriasis have contributed to a better understanding of the burden of the disease. However, further research is required to fill existing gaps in understanding the Epidemiology of Psoriasis and trends in Incidence over time.Journal of Investigative Dermatology advance online publication, 27 September 2012; doi:10.1038/jid.2012.339.