It is imperative to identify the cause of cerebrospinal fluid (CSF) leak due to the major risk of infectious complications. Mainly the consequence of a skull base or facial trauma, its most frequent symptom is rhinorrhea. It represents a real diagnostic, clinical and radiological challenge. Two extreme situations raise different problems: either CSF leak is active, with important facial damage involving frontal, ethmoidal or sphenoidal sinuses and petrous bone; in such cases, evaluation by CT is sufficient and easy. Or the leak has dried up, there is no evidence of bony fracture; it is imperative to localize the exact site of the bony or dural defect: CT in axial and coronal planes with thin slices, computerized tomographic cisternography with non ionic water soluble contrast media in order to exhibit the leak in the paranasal sinuses. In some cases however, pitfalls still occur in the determination of such meningeal fistulae.