A 59-year-old woman undergoing narrowband UVB phototherapy for treatment of psoriasis presented suddenly with tense blisters on both hips. The blisters were asymptomatic and disappeared within 24 hours. Histopathology together with a negative porphyrin screen made the diagnosis of pseudoporphyria. Blood tests including a full blood count, urea and electrolytes, liver function tests and antinuclear autoantibodies were normal. The patient was otherwise healthy; there was no history of extensive sun exposure, sunbeds or medication with non-steroidal anti-inflammatory drugs. This presentation of pseudoporphyria secondary to narrowband UVB radiation is unusual, as UVB radiation is not known to be associated with pseudoporphyria.