In the natural history of infantile extracerebral fluid collections, subarachnoid fluid collection itself is regarded as a benign lesion, and surgical treatment is not indicated. As this condition is age-related and self-limiting, spontaneous resolution can be expected in most cases by 2-3 years of age. However, out of 20 cases of infantile subarachnoid fluid collection in an 8-year period, 3 infants developed subdural hematoma. Infantile subarachnoid fluid collection seems to be prone to complicate subdural hematoma. Surgical treatment should be considered when subarachnoid fluid collection is complicated by subdural hematoma due to arachnoid ruptures or tearing of the bridging veins. Therefore, all patients should be observed closely and measures should be taken to prevent head trauma since it may precipitate subdural hematoma.