Numerous reports have shown that psoriasis is associated with obesity and leptin. However, few reports are available on the association between serum leptin levels and leptin gene expression in SAT of psoriasis patients. To clarify this point, we examined serum leptin levels and expression levels of leptin messenger RNA (mRNA) in subcutaneous adipose tissue (SAT) of psoriasis patients. 17 psoriasis vulgaris patients and 6 non-obese control patients who underwent skin surgery were enrolled in this study. We measured serum leptin levels. SAT samples in psoriasis patients were taken from beneath the lesional psoriatic skin at the time of skin biopsy. Leptin mRNA expression in SAT was measured using quantitative real-time reverse transcription polymerase chain reaction (real-time RT-PCR) amplification. Leptin mRNA expression showed a positive correlation with serum leptin levels and BMI. We classified psoriasis patients into two groups according to BMI: the group of non-obese psoriasis patients (BMI < 25, n = 7), and the group of obese psoriasis patients (BMI ≥ 25, n = 10). PASI score, serum leptin levels and Leptin mRNA expression in SAT were significantly higher in the obese psoriasis patients than in the non-obese psoriasis patients. Leptin mRNA expression in SAT was correlated with circulating levels of leptin, the severity of psoriasis, and obesity in psoriasis patients. Serum leptin levels and leptin mRNA expression levels in SAT of non-obese psoriasis patients were not significantly different from those of non-obese controls. The altered secretion of leptin by SAT may be related to the severity of psoriasis.