The verified presence of a glioblastoma multiforme (GBM) tumor in the motor area of the brain, in a patient lacking preoperative neurological deficit, offers no certainty that the tumor can be radically removed without the possibility of causing postoperative motor deficit. We present a series of 60 patients hospitalized at the Clinical Department of Neurosurgery, Clinical Center of Serbia in Belgrade between October 2011 and February 2015, harboring tumors located within and in the vicinity of the motor zone of the brain. By using Karnofsky's index (KI), the pre- and postoperative conditions of the patients were evaluated. Regarding electrical stimulation of the motor cortex, significantly lower values of the electrical current intensity, frequency, and pulse wave duration (p < 0.01) were needed for triggering motor response in case of GBM tumor compared to a slowly growing tumor (low-grade). Patients with low-grade gliomas (LGG) had statistically significantly higher KI values pre- and postoperatively than patients with GBM (p < 0.01). Using electrical stimulation of the cortex, a higher grade of resection of LGG could be achieved as compared with the group presenting with GBM (χ² = 5.281; df = 1; p < 0.05). Our findings and review of the results reported by other authors underline the necessity of routine application of electrical stimulation of the cerebral cortex in order to identify the primary motor field (M1).