This study focused to investigate a possible association of extensive umbilical hypercoiling (displaying an umbilical coiling index [UCI] of at least 1.0 coils/cm), clinical outcome, and associated pathoanatomical placental lesions. Of the 771 singleton placentas from the second and third trimesters submitted for pathoanatomical evaluation, 15 cases (2%) displayed extensive hypercoiling. There was an association of excessive hypercoiling with hypotrophy of fetuses and children (11 cases) and fetal demise (12 cases). Thin cord syndrome and umbilical stricture were observed in 9 cases and 4 cases, respectively. Seven of the 15 cases with excessive umbilical hypercoiling showed increased placental fibrin deposition (47% of the cases with hypercoiling), in 4 cases sufficient for rendering the diagnosis of massive perivillous fibrin deposition. Signs of maternal vascular malperfusion (n = 6) and chorangiosis (n = 2) were also detected in cases with hypercoiling. Recurrence of excessive umbilical hypercoiling was observed in 2 families, suggesting a genetic predisposition for the development of this lesion. Extensive hypercoiling could be a hitherto underrecognized pathogenetic factor for the development of massive perivillous fibrin deposition. A high UCI measured in the second trimester by ultrasound may be predictive of fetal hypotrophy, and intensified fetal monitoring is warranted, particularly if there is a history of hypercoiling and adverse fetal outcome.