Erythropoietic protoporphyria (EPP) is a rare inherited disorder of heme biosynthesis mostly caused by a deficient activity of the enzyme ferrochelatase (FECH), and consequent accumulation of protoporphyrin (PP) in various tissues. Clinical manifestations include a childhood onset, cutaneous photosensitivity and, sometimes, hepatobiliary disease. We report a 16-year-old male with EPP characterized by acute episodes of painful photosensitivity since early infancy, permanent changes in the photoexposed skin, microcytic anemia, thrombocytopenia, and mild hepatic dysfunction. His 18-year-old sister presented less acute symptoms with no chronic changes. Lesional biopsy disclosed perivascular deposition of PAS positive hyaline material. Rimington-Cripps test was positive and PP erythrocyte levels were >9,000 μg/L (N<1,600), but normal in their parents and younger brother. Genetic studies in both patients and their mother revealed heterozygosity for a novel mutation (c.1052delA) in FECH gene of both children, and heterozygosity for the hypomorphic allele IVS3-48T>C in all of them. This confirms the "pseudodominant" inheritance pattern usually observed, explained by the combined presence of a disabling FECH mutation and a common intronic polymorphism affecting the counterpart allele (IVS3-48T>C). Phenotypic heterogeneity for this genotype explains the divergent clinical presentation. This is the first description of a Portuguese family with EPP characterized at the molecular level.