OBJECTIVE Psoriasis is a chronic inflammatory skin disease for which no specific reason has been found although various reasons have been suggested. Helicobacter pylori is a Gram-negative bacterium, which is essentially considered the cause of acute and chronic gastritis. Recently, several reports have suggested that H pylori could play a role in triggering psoriasis. The aim of this study was to determine the relationship between H pylori seropositivity and psoriasis. METHODS This was a case-control study performed on patients with psoriasis vulgaris and healthy individuals in Fatemiye Hospital (referral center for the treatment of skin diseases), Semnan, Iran, during April 2011 to April 2012. METHODS A case-control study including 61 patients with psoriasis vulgaris (case group) and 61 healthy individuals (control group) without any known gastrointestinal complications were enrolled. All cases were tested for H pylori infection with serology (immunoglobulin G [IgG] anti-H pylori) using the enzyme-linked immunosorbent assay method. RESULTS Ten (16.4%) of the psoriatic patients and 8 (13%) of the control groups had an H pylori seropositive test result; the average of IgG serum level was 17.3 IU/ML in psoriatic patients and 16.1 IU/ML in the control group. The difference of serum level between the 2 groups was not meaningful (P=.302). CONCLUSIONS Our finding indicated that there was neither a significant relationship between psoriasis and the serum level of IgG anti-H pylori, nor a significant relationship between psoriasis severity and the serum level of IgG anti-H pylori. Further studies should be designed to find out whether infection with H pylori is one of the reasons causing or aggravating psoriasis.