The finding of a colloid cyst on neuroimaging is often incidental. These lesions are usually located at the foramen of Monro, are hyperdense on CT scans, and generally demonstrate signal intensity of water on MR images, although this depends on their content. When symptomatic, they frequently present with headaches and nausea due to an obstructive hydrocephalus. The authors describe a case of a giant colloid cyst in a patient presenting with complete left-sided vision loss and progressive memory loss, two very atypical findings in colloid cyst presentation. Imaging findings were also atypical, and this case proved to be a diagnostic dilemma because of its clinical and radiological presentation. Histopathological investigation was of utmost importance in the final diagnosis of a colloid cyst. To the authors' knowledge this colloid cyst is larger than any other described in the literature.