Optic nerve glioma has been a topic of great interest and controversy, particularly with respect to its tendency to invade the optic chiasm. This case report demonstrates histologically verified optic nerve glioma in an otherwise healthy 5-year-old girl. MRI revealed sequential prechiasmal, chiasmal, and postchiasmal disease during the untreated course of 18 months. The authors also discuss the results obtained with a specific immunohistochemical technique, the mindbomb homolog 1 (MIB-1) labeling index, and speculate that this information, if known early in the course of disease, might influence early surgical decision-making.