Recent advances in the molecular understanding of the porphyrias now offer specific diagnosis and precise definition of the types of genetic mutations involved in the disease. Molecular diagnostic testing is powerful and very useful in kindred evaluation and genetic counselling when a disease‐responsible mutation has been identified in the family. It is also the only way to properly screen asymptomatic gene carriers, facilitating correct treatment and appropriate genetic counselling of family members at risk. However, it should be noted that DNA‐based testing is for the diagnosis of the gene carrier status, but not for the diagnosis of clinical syndrome or severity of the disease, e.g. an acute attack. For the diagnosis of clinically expressed porphyrias, a logical stepwise approach including the analysis of porphyrins and their precursors should not be underestimated, as it is still very useful, and is often the best from the cost‐effective point of view.