Alexia without agraphia is a rare disconnection syndrome characterized by the loss of reading ability with retention of writing and verbal comprehension. We report a patient who developed alexia without agraphia after undergoing a biopsy for a malignant glioma involving the left thalamus. A 15-year-old right-handed male presented with 3 days of severe headache, and vomiting, and 1 month of blurry vision in his right visual field. Magnetic resonance imaging of the brain disclosed a large exophytic mass originating in the left thalamus, with mass effect and hydrocephalus. The patient underwent biopsy of the left thalamic mass via a transcallosal approach. Postoperatively, the patient complained of inability to read or identify letters. Examination revealed alexia without agraphia. The syndrome of alexia without agraphia can be rarely caused after surgery. A transcallosal procedure through the splenium of the corpus callosum may disrupt the visual association fibers traveling from the right occipital cortex to the left angular gyrus. In our case the syndrome occurred because of a preexisting right homonymous hemianopia resulting from a left thalamic tumor.