Increasing use of neuroimaging in children has led to more incidental findings of CNS mass lesions, the management of which is uncertain. The authors' aims in this study are to describe these mass lesions and their evolution, as well as to discuss the management options and determine the prevalence of incidental CNS mass lesions at their pediatric clinic. A retrospective study was undertaken in children with primary CNS tumors who were younger than 18 years old and were admitted to the University Children's Hospital of Zurich, Switzerland, between January 1995 and December 2010. In 19 (5.7%) of 335 patients with newly diagnosed CNS tumors, the diagnosis of a CNS mass lesion was an incidental finding. Reasons for obtaining neuroimages in these 19 patients were head trauma (in 6 patients); research protocols (in 3); nasal/orbital malformations (in 2); endocrinological and psychiatric evaluations (in 2); and vertebral bone anomaly without neurological signs, absence seizures, congenital ataxia, recurrent vomiting, developmental delay, and "check-up" at the explicit request of the parents (in 1 patient each). Seven patients underwent immediate surgery for low-grade glioma (4 patients) and craniopharyngioma, ependymoma, and choroid plexus papilloma (1 patient each); and 12 were treated conservatively or were observed. Ten of 12 conservatively treated patients remained stable (median follow-up time 1.8 years) and the other 2 underwent delayed surgery because of tumor progression (medulloblastoma in one patient and fibrillary astrocytoma in the other). Clinicians are increasingly challenged by the discovery of incidental CNS mass lesions. A subgroup of such lesions (with typical imaging patterns such as tectal glioma and dysembryoplastic neuroepithelial tumor) can be monitored conservatively, clinically, and radiographically. Future prospective studies are needed to define optimal management strategies based on larger collections of natural histories, as well as to assess the true prevalence of incidental CNS mass lesions.