Postnatal closure of the ductus arteriosus is a complicated two-phase process involving functional and structural changes. So far, the precise mechanisms regulating this process are not fully understood. A growing body of evidence from recent studies suggests that platelets play a key role in inflammatory processes including ductal closure via interaction with endothelial cells. The aim of this study is to assess whether a relationship exists between the occurrence and/or closure of hemodynamically significant ductus arteriosus (HSDA) and platelet parameters (platelet count, circulating platelet mass, mean platelet volume, platelet distribution width) in preterm newborns. This single-center, retrospective study included 824 premature infants between 24 and 34 gestational weeks, evaluated by echocardiography at postnatal 72-96 h. Infants with and without HSDA (nU208 vs. nU616) were compared in terms of platelet parameters recorded within the first 3 days of life. Oral or intravenous ibuprofen was commenced for medical treatment, and echocardiography was repeated 24 h thereafter to determine ductal closure. No statistically significant difference could be demonstrated between the groups in terms of baseline platelet parameters. HSDA was independently associated with early-onset neonatal sepsis. Thrombocytopenia, low circulating platelet mass, high platelet distribution width, or high mean platelet volume could not be demonstrated as a risk factor for HSDA. None of the platelet parameters had an influence on ductal closure after medical treatment. Unlike most reports in the literature, presence of HSDA was not associated with any platelet parameter in our study. We could not demonstrate an association between any platelet parameter and either persistence or closure after medical treatment. Copyright (C) 2017 Wolters Kluwer Health, Inc. All rights reserved.