Spontaneous subaponeurotic fluid collection (SSFC) is an uncommon and newly described entity of unknown etiology, observed in infants less than 1 year of age. The authors report on series of infants who presented to the Hospital for Sick Children (HSC) with SSFC, focusing on the natural history of this condition. METHODS Data from the Hospital for Sick Children were retrospectively reviewed for the period between January 2004 and June 2015. Patient age and sex, birth history, medical history, laboratory findings, and symptoms were reviewed. SSFC location, imaging characteristics, management, and outcome were also analyzed. A MEDLINE and Embase literature search was performed on the condition, yielding previously reported cases of SSFC in the English language. RESULTS Nine cases involving patients who presented with SSFC during the study period were identified. The patients were 4 male and 5 female infants (age range 5 weeks to 11 months). All cases of SSFC developed spontaneously over a period of days, and the infants had no history of injuries, trauma, or hair manipulation in the immediate period preceding the development of the subgaleal collections. Six patients underwent remote forceps- or vacuum-assisted instrumented births, although none of the patients developed scalp collections or skin discoloration immediately after birth. All of the cases were managed conservatively on an outpatient (6 cases) or inpatient (3 cases) basis. In 1 case, the size of the fluid collection fluctuated over 4 months, but in all of the cases, the collections resolved spontaneously without structural or infectious complications. CONCLUSIONS This is the largest series describing SSFC to date and summarizes 9 cases managed at a large academic neurosurgical center. Although the specific pathophysiology of SSFC remains unknown, in some cases the condition may be associated with a remote history of instrumented delivery. SSFC occurs spontaneously without immediate preceding trauma, and an extensive hematology or child abuse workup is not necessary. A conservative approach with outpatient follow-up is advocated 1).