Premature ovarian insufficiency (POI) is a life-changing diagnosis, with profound physical and psychological consequences. Despite the description of different genetic, immune and iatrogenic factors of POI, the etiology of most cases of this disease are unexplained, and optimal management strategies are still unclear. Recent data showed that POI may have a long period of oligomenorrhea before the fully developed form (complete ovarian failure stage), with the occurrence of amenorrhea and climacteric symptoms. The main problem in the recognition of early stages of POI is the lack of proper diagnostic criteria. Patients with an undiagnosed occult form of POI may present with menstrual irregularities, unexplained infertility or repeated IVF failures. We evaluated 23 patients with unexplained oligomenorrhea and/or infertility. After a proper evaluation of these patients, a low ovarian reserve was identified, and an occult form of POI was diagnosed. © 2016 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group.