BACKGROUND: Transient sub-aponeurotic fluid collections are rarely recognized lesions that may be frequently related to traumatic labor and occur within weeks after birth. Their etiology has remained uncertain. METHODS AND RESULTS: Here we report on five new cases with typical clinical findings and normal neuroimaging. A detailed analysis of the lesion aspirates was performed in three patients, always revealing beta(2)-transferrin and high concentrations of beta-trace protein. CONCLUSIONS: This indicates that cerebrospinal fluid leakage contributes to this rare condition. All lesions disappeared spontaneously within 2-5 months so that conservative treatment seems appropriate.