Subclinical deficiency of pituitary hormones represents an intermediate situation among normal pituitary secretion and overt hypopituitarism. Clinical hypopituitarism is associated with impaired morbidity and mortality, but there are not many studies on these topics in the subclinical setting. Moreover, clinical manifestations and diagnosis criteria are not well defined, so this entity is probably an underdiagnosed disorder. Long-term controlled studies are needed to establish a correct definition of subclinical hypopituitarism and to know its clinical implications, optimal methods of diagnosis, and indications for substitutive treatment. This review will focus on the evidence related to epidemiology, clinical manifestations, diagnosis, and treatment of subclinical hypopituitarism.