Hepatoerythropoietic porphyria is characterized by an early beginning of severe photosensitivity, with an increase in urinary uroporphyrin excretion and other porphyrins, high isocoproporphyrin fecal levels and an accumulation of protoporphyrin in erythrocytes. It is caused by a dramatic decrease in the activity of the uroporphyrinogen decarboxylase. We report a clinical, biochemical and enzymatic study in a family, where a 2-year-old girl suffers from a hepatoerythropoietic porphyria, and the patient's maternal uncle from a porphyria cutanea tarda. We discuss the relationship between these diseases and their known mutations.