Objective: To analyze the syndrome of persistent low levels of hCG in terms of its etiology, classification, diagnosis, and management. Design: Retrospective analysis. Setting: Center for Trophoblastic Disease in Czech Republic, Institute for Care of Mother and Child, Prague, Institute of Postgraduate medical education, IPVZ, Prague Methods: An analysis of the syndrome of persistent low levels of hCG recorded in CTN in 29 women in the years 1979-2005 by the immunoluminesence method which can quantitatively assess variable levels of hCG in blood and urine. A comparison was made of our findings with results of a similar studies having been done in England and USA. Results: Persistent low levels of hCG (PLL) can be differentiated according to cause. 1. PLL-F False positive, also known as Phantom hCG,often caused by heterogenous antibodies. 2. PLL-HOf hypophysial origin, mainly in perimenopause and menopause. 3. PLL-QQuiescent with trophoblastic disease in history, of trophoblastic origin. 4. PLL-U Undetermined, in history without trophoblastic disease, but in the past with physiological or pathological pregnancy. Assuming also to be of trophoblastic origin. All types of PLL lead in practice to the wrong diagnosis of trophoblastic disease and to a high percentage (40-80%) of needless chemotherapy and operations. In no case of PLL did chemotherapy or operations have an effect on PLL and thus are contraindicated. PLL-Q and PLL-U require continuous clinical and laboratory monitoring and repeated examinations with sophisticated visualization methods. The percentage of developing malignant trophoblastic tumors after PLL-Q and PLL-U is unclear. Extreme incidence was established in 7-25%. PLL-Q and PLL-U are considered as a marker of persistent trophoblastic invasion. Its detection by visualization methods in any organ localization before it turns into a limited solid tumor is excluded by it microscopic dissociative structure. Conclusion: The syndrome of persistent low levels of hCG (PLL) lately affects all gynecological and obstetrical workplaces. According to cause it can be divided into: 1. PLL false positive, 2. PLL of hypophysial origin, 3.PLL quiescent with trophoblastic disease in the history, 4. PLL undetermined, in history without trophoblastic disease. In the last two items mentioned above we assume to be of trophoblastic origin.Their morphological base is persistent trophoblastic invasion.The syndrome of PLL often leads to the wrong diagnosis of trophoblastic disease and to needless chemotherapy and operations. In this work was described the diagnosis of PLL, its classification,cause, and management. The percentage of PLL turned into malignant trophoblastic disease is unknown and ranges from 7-25% and requires monitoring in an accredited, national center for trophoblastic disease.

        Key words: trophoblastic disease, chorionic gonadotrophin, resistent low levels of hCG