Turner syndrome (TS) is a noninherited genetic disorder caused by the absence of one or part of one X chromosome. It is characterized by physical and cognitive phenotypes that include motor deficits that may be related to neuroanatomical abnormalities of sensorimotor pathways. Here, we used transcranial magnetic stimulation (TMS) and cortical thickness analysis to assess motor cortex excitability and cortical morphology in 17 individuals with TS (45, X) and 17 healthy controls. Exploratory analysis was performed to detect the effect of parental origin of the X chromosome (Xmat, Xpat) on both measures. Results showed that long-interval intracortical inhibition was reduced and motor threshold (MT) was increased in TS relative to controls. Areas of reduced thickness were observed in the precentral gyrus of individuals with TS that correlated with MT. A significant difference between Xmat (n = 11) and Xpat (n = 6) individuals was found on the measure of long-interval intracortical inhibition. These findings demonstrate the presence of converging anatomical and neurophysiological abnormalities of the motor system in X monosomy. Hum Brain Mapp, 2013. © 2011 Wiley Periodicals, Inc.