Psoriasis vulgaris is considered a chronic inflammatory disease, but its immunopathogenesis has not been well understood. The tumor necrosis factor alpha-induced protein 3 (TNFAIP3) gene functions in negative-feedback regulation of inflammation, and its single nucleotide polymorphism is associated with psoriasis. However, the relationship between the expression level of the TNFAIP3 gene in immune cells and psoriasis is not known so far. In the present study, TNFAIP3 mRNA expression levels in peripheral blood mononuclear cells from 44 patients with psoriasis vulgaris and 30 healthy controls were determined using real-time reverse transcription-PCR analysis. We found that expression of TNFAIP3 mRNA in all patients negatively correlated with the psoriatic area and severity index (PASI) (r = -0.5126; P = 0.0004) as well as with the percentage of body surface area affected by psoriasis (r = -0.5013; P = 0.0005). Patients were divided into mild and severe groups based on the mean PASI score. Expression of TNFAIP3 mRNA in the mild group was higher than that in the severe group (P = 0.0064). Moreover, compared with that in healthy controls, the expression of TNFAIP3 mRNA in the mild group was significantly upregulated (P = 0.0004), but the expression of TNFAIP3 mRNA in the severe group was not. These results suggest that the expression level of TNFAIP3 plays an important role in the pathology of psoriasis vulgaris and that the loss of upregulation of TNFAIP3 expression may contribute to the severity of psoriasis vulgaris.