['The carcinogenic potential of 8-methoxypsoralen photochemotherapy (psoralen-UVA [PUVA]) is correlated with the total number of treatments and cumulative UVA dose applied during oral PUVA therapy.', 'We sought to determine whether reducing treatment frequency and UVA dose affects the therapeutic efficacy of oral PUVA for patients with chronic plaque psoriasis.', 'This was a prospective, randomized, half-side study performed in a photodermatology department in a dermatology hospital. Eighteen consecutive patients with chronic plaque psoriasis received paired PUVA regimens (0.5 minimal phototoxic dose [MPD] 4 times/wk vs 1 MPD twice/wk, 0.5 MPD twice/wk vs 1 MPD twice/wk, and 0.5 MPD twice/wk vs 0.75 MPD twice/wk). The PUVA regimens were assessed for reduction of Psoriasis Area and Severity Index (PASI) score and the number of treatments and cumulative UVA dose required to reduce PASI score to defined end points (ie, PASI reductions of 25%, 50%, and 75%) or to induce complete remission (PASI < 3).', 'Reducing the number of treatments while maintaining the same UVA dose per week did not reduce overall therapeutic efficacy. Reducing the number of treatments to twice a week and reducing the UVA dose from 1 MPD to 0.75 or 0.5 MPD per treatment only slightly affected intermediate therapeutic efficacy (between the second and seventh weeks of therapy) but had no effect on final clearance rates. The time to complete clearance did not significantly differ between regimens. The mean cumulative UVA dose was significantly lower for the least intensive dose regimen (0.5 MPD twice/wk) than for the more intensive regimens.'] Does reduction of treatment frequency and UVA dose substantially compromise the antipsoriatic effect of oral psoralen-UVA?