Three and five times weekly narrow-band TL-01 (311–313 nm) ultraviolet (UV) B phototherapy regimens for chronic plaque psoriasis were compared in a randomized, observer-blinded, half-body, within-patient paired study. Twenty-one patients [13 men, eight women, age range 21–68 years, skin phototypes I (two patients), II (14) and III (five)] entered the study. Sixteen reached clearance or minimal residual activity (MRA) on both sides. Of the other five, three withdrew because they did not reach clearance or MRA on the 5 × weekly side by a maximum of 30 treatments, one when he was satisfied with moderate improvement and one because of repeated failure to attend. Those who completed treatment reached clearance or MRA after a median of 35 days with 5 × weekly treatment compared with 40 days with 3 × weekly treatment (P = 0.007), but required a median of 23.5 compared with 17 UVB exposures (P = 0.001) and 94 minimal erythema dose multiples (MEDs) compared with 64 MEDs (P = 0.01). Fifteen (of 16) developed at least one episode of well-demarcated erythema during 5 × weekly treatment compared with just three of 16 treated 3 × weekly (P < 0.001). There was no significant difference between regimens in duration of remission. For this skin phototype I–III population, the more rapid clearance of psoriasis with 5 × weekly phototherapy is not, for the majority of patients, sufficient to justify the extra exposures and higher UVB dose. We no longer use 5 × weekly phototherapy for psoriasis.