Pustulosis palmaris et plantaris (PPP) is a chronic recurrent dermatitis characterized by intraepidermal pustules with erythematous scaling on the palms and soles. PPP shares many characteristics with psoriasis, but has a different genetic background. T helper 17 cells (Th17) have an important role in the pathogenesis of psoriasis. In psoriasis, regulatory T cells (Treg) are dysfunctional and circulating Th17 are increased. Whether Th17 are involved in PPP, however, is unclear. Therefore, we examined the Th17 population in peripheral blood mononuclear cells (PBMC) of patients with PPP. Foxp3(+) Treg was also analyzed. We examined circulating Th17 and Treg in the peripheral blood of PPP patients. PBMC were obtained from healthy volunteer controls (n = 26, mean ± SD age 33.11 ± 9.80 years) and PPP patients (n = 24, age 55.00 ± 12.26 years). The proportion of Th17 among the PBMC was 2.52 ± 0.811% (mean ± SD) in healthy controls and 3.23 ± 1.45% in PPP patients. The proportion of Th17 in the PPP patients was significantly higher than that in the healthy controls (p < 0.05, Student's t test). PPP patients had significantly fewer Treg (5.69 ± 1.86%) than healthy controls (7.10 ± 1.78%). Th17 was inversely correlated with Treg.