Thymus and activation-regulated chemokine (TARC) is designated as a T-helper 2-type chemokine and its expression is upregulated in patients with atopic dermatitis. Previous studies reported that serum TARC levels in patients with psoriasis vulgaris (PsV) were comparable with those in healthy controls. However, the association of clinical severity of psoriasis with serum TARC levels and serum TARC levels in patients with psoriatic arthritis (PsA) or generalized pustular psoriasis (GPP) have never been reported. We investigated the association of serum TARC level with psoriasis by the type of psoriasis, and examine correlations of serum TARC levels with clinical severity scores and other results of blood tests. Data on 75 patients (51 men and 24 women; PsV, 30 patients; PsA, 29 patients; GPP, 16 patients) were analyzed. The serum TARC level was significantly higher in patients with GPP than in patients with PsV and patients with PsA. There was a positive correlation between serum TARC level and Psoriasis Area and Severity Index score (r = 0.3499, P = 0.0030). The serum TARC levels decreased after treatment in GPP patients. Our study revealed that the serum TARC level can potentially be one of the biomarkers reflecting the severity or systemic inflammation caused by psoriasis in patients with psoriasis, although not as much as in patients with atopic dermatitis. Furthermore, serum TARC levels were high in patients with GPP. Those were decreased by treatment, suggesting that serum TARC levels could be utilized as an objective biomarker to evaluate a therapeutic effect in individual GPP patients. Further accumulation of cases and further research are needed to elucidate the role of TARC in psoriasis.