Except for a few particular conditions, the diagnostic evaluation of hyperprolactinemia is easy since the routine use of magnetic resonance imaging (MRI) scan has permitted to identify even small microadenomas. Other conditions include the identification of large PRL molecular complex, dimers, trimers or polymers of PRL, called "big or big-big PRL", and of PRL autoantibodies and the biochemical finding of "high dose PRL hook effect". Finding elevated serum PRL levels should be considered as the beginning and not the conclusion of a diagnostic evaluation: first, a careful anamnesis should exclude possible physiologic, pharmacologic and organic causes of hyperprolactinemia; second, possibly one laboratory only, undergoing regularly quality controls, should analyze blood samples; serial serum PRL measurements at 0, 30, 60 min is a valuable and simple measure to identify stress-related hyperprolactinemia. In the past two decades several pharmacological tests were used in order to distinguish between small microprolactinomas and "non-tumoral hyperprolactinemia": the controversial results of these tests together with the availability of MRI has excluded all pharmacological tests in the work-up of hyperprolactinemia. MRI is preferred to computed tomography (CT) due to its better definition of very small lesions in the pituitary sella and better anatomical definition prior to surgery. Finally, once the diagnosis of prolactinoma is suspected, patients should be referred to a specialist centre for further assessment and treatment.