The porphyrias are a group of inborn or acquired disorders of haem synthesis that can result in neurovisceral or dermatological symptoms. Diagnosis is usually made using a combination of clinical presentation and biochemical parameters. This case report describes a 25-year-old woman clinically presenting with a rash and then found to have elevated porphobilinogen concentrations in her urine. The initial presumptive diagnosis of variegate porphyria was not supported by analysis of her plasma, urine and faeces, which suggested a combination of acute intermittent porphyria and porphyria cutanea tarda. Sequencing of the hydroxymethylbilane synthase and uroporphyrinogen decarboxylase genes confirmed the relatively rare diagnosis of dual porphyria, and revealed a novel uroporphyrinogen decarboxylase mutation.