In patients with severe chronic atopic dermatitis (AD), both photochemotherapy [psoralen ultraviolet A (PUVA)] and narrow-band (TL-01) UV B phototherapy have been reported to be very effective. As no data exist on the relative therapeutic efficacy of these two regimens, we performed a randomized investigator-blinded half-side comparison study on 12 patients with severe chronic AD. Half-side irradiation with threshold erythemogenic doses of 8-methoxypsoralen bath-PUVA and narrow-band UVB was performed three times weekly over a period of 6 weeks. The severity of the disease was assessed separately for the paired halves of the patients’ bodies by a modified SCORAD score at baseline and after 2, 4 and 6 weeks of treatment. Ten of the 12 patients completed the trial. All but one showed marked improvement or complete remission with both treatments. The mean baseline SCORAD score decreased by 65·7% by the bath-PUVA treatment and by 64·1% by the narrow-band UVB treatment (P = 0·48). No serious adverse reactions to either of the two regimens were observed. Our data confirm the high efficacy of bath-PUVA and narrow-band UVB phototherapy in the treatment of patients with chronic severe AD. Both regimens appear to be equally effective when administered in equi-erythemogenic doses.