A 3-year-old male with a history of autism along with cognitive, language, and behavioral delays presented to the emergency department after falling 4 feet from a window. Head computerized tomography (CT) revealed a 5 x 5 x 4 cm AC of the left frontal convexity with subjacent mass effect. Before the fall, he had delays in cognitive advancement with difficulty following commands, naming objects, and making eye contact. He was able to ambulate with assistance but unable to climb stairs. He also banged his head against walls frequently while screaming and it was unclear if this was secondary to headaches. The patient received physical, occupational, and behavioral therapy through early intervention therapies with no real improvement. On neurological examination, he made no eye contact, did not follow commands, was not cooperative, did not speak or verbalize, but did demonstrate symmetric movement. The patient's family stated that he had undergone neuropsychiatric testing which diagnosed autism but the patient's family did not provide reliable follow-up with us; we were unable to obtain this report. The patient was lost to follow-up for 6 months, and on representation, a magnetic resonance imaging (MRI) was obtained which demonstrated a 5.6 x 5.2 x 4.5 cm left frontal AC with associated mass effect on the adjacent parenchyma and frontal horn of the left lateral ventricle. Ophthalmological assessment revealed no papilledema. The patient underwent a left frontal craniotomy for microsurgical fenestration of the AC with excision of the cyst wall without complication. At 10-day follow-up, his parents reported much calmer behavior with no further labile outbursts and less head banging. At 1 month follow-up, his parents reported significant improvement in cognitive function whereby he was following instructions in computer games and solving multistep problems. His behavior was completely altered and more appropriate for 3 years old and he was making eye contact and interacting with multiple examiners while playing games with them as well. He was following simple commands and no longer banging his head on walls. He was naming objects and persons at home and in clinic. At 3 months follow-up, his behavior continued to improve, most noticeably, with additional verbalization and interaction and eye contact with family and strangers. Unfortunately, the patient was lost to further follow-up [Figures 1-5].