Up to now, navigated transcranial magnetic stimulation (nTMS) has been used for motor mapping in the vicinity of rolandic brain lesions. Recently, nTMS has also been suggested to be useful in mapping human language areas. The authors describe the case of a left-handed patient with a left-side glioblastoma within the opercular inferior frontal gyrus who presented with severe motor aphasia. Preoperative functional MRI (fMRI) indicated speech dominance of the right hemisphere and did not show any language-related activation in the vicinity of the tumor. Navigated TMS, however, showed a significantly higher rate of induced speech arrests for the left than for the right. Left-side direct cortical stimulation induced clear speech arrests during awake surgery. This case suggests that nTMS may be useful for preoperative speech mapping in tumors affecting the anatomy, vasculature, and brain oxygen levels and therefore impairing fMRI reliability.