The expression of cyclin D1 and p16 was evaluated before and after 24 sessions of psoralen ultraviolet A (PUVA) therapy (n = 11) or narrowband UVB (NB-UVB) therapy (n = 14) in patients with psoriasis and a mean age of 44 years. Ten healthy age- and gender-matched controls were also included in the study. Prephototherapy, the mean value of cyclin D1 in psoriasis patients was significantly (P < 0.001) higher than in controls while p16 levels were significantly lower (P < 0.001). Following treatment, cyclin D1 levels decreased significantly (P < 0.01) and p16 levels significantly increased (P < 0.001). Up- and downregulation of these two agents may play a role ...