In this study, we examined the expression of HDAC1, SIRT1, and the proliferation markers p63 and proliferating cell nuclear antigen (PCNA) in guttate and plaque psoriasis using immunohistochemistry to investigate whether they are dysregulated in psoriatic skin and if there is any difference between subtypes of psoriasis. The gene discussed is PCNA; the disease is psoriasis vulgaris.