Teratomas represent 0.5% of all intracranial tumors. These benign tumors contain tissue representative of the three germinal layers. Most teratomas are midline tumors located predominantly in the sellar and pineal regions. The presence of a teratoma in the cavernous sinus is very rare. Congenital teratomas are also rare, especially those of a cystic nature. To our knowledge, this would be the first case report of a congenital, rapidly growing cystic teratoma within the cavernous sinus. A three-month-old boy presented with a past medical history of easy irritability and poor oral intake. A magnetic resonance image (MRI) scan of the head disclosed a large expanding cystic tumor filling the right cavernous sinus and extending into the pterygopalatine fossa through the foramen rotunda. These scans also demonstrated a small area of mixed signal intensity, the result of the different tissue types conforming to the tumor. Heterogeneous enhancement was seen after the infusion of contrast medium. However, this was a cystic tumor with a large cystic portion. Thus, a presumptive diagnosis of cystic glioma was made. With the use of a right frontotemporal approach, extradural dissection of the tumor was performed. The lesion entirely occupied the cavernous sinus, medially displacing the Gasserian ganglion and trigeminal branches (predominantly V1 and V2). The lesion was composed of different tissues, including fat, muscle and mature, brain-like tissue. The tumor was completely removed, and the pathological report confirmed the diagnosis of a mature teratoma. There was no evidence of recurrence. Despite the location of the lesion in the cavernous sinus, total removal can be achieved with the use of standard microsurgical techniques.