With the advent of modern diagnostic tools for neuroimaging, the incidental detection of pineal cysts in asymptomatic subjects has increased. Only rarely do pineal cysts present with the clinical signs and symptoms of increased intracranial pressure or with neurological deficits in relation to compression and distortion of the adjacent nervous structures and cerebrospinal fluid pathways. While asymptomatic cysts are considered to be normal variants for which no further investigations are usually required, surgical treatment is suggested for symptomatic cysts, with the goal of eliminating the block in the cerebrospinal fluid circulation and/or the mass effect exerted by the lesion. In this report we describe a pediatric case of symptomatic pineal cyst, revealed by repeated episodes of headache caused by secondary obstructive hydrocephalus. Following an endoscopic third-ventriculostomy, serial magnetic resonance imaging studies demonstrated that not only had the ventriculomegaly resolved but also that the pineal cyst had regressed over time. A to-and-fro movement of fluid through the cyst wall, the direction of which depends on the equilibrium existing between the inner pressure of the cyst and the outer cerebrospinal fluid pressure, is suggested as a possible mechanism accounting for this unexpected result--to our knowledge, the first reported in literature.