Fifty-one patients with cerebrospinal fluid rhinorrhea were evaluated at the Mayo Clinic from 1974 to 1977. The causes of the leak were fairly even distributed among postoperative, traumatic unrelated to previous surgery, and nontraumatic. The slightly fewer patients with a traumatic cause compared with those reported in most series reflects the referral patterns and surgical nature of the practice at the institution. Three-fourths of the patients had plain films of the skull, although the site of the leak was identified in only 21% of them. Two-thirds of the patients had tomography, which was helpful in 53%, especially in 10 of the 13 patients with traumatic nonpostoperative cerebrospinal fluid rhinorrhea. Posteroanterior tomography generally was more helpful than lateral tomography, except in leaks around the frontal sinuses. Radioisotope cisternography with intranasal pledgets helped localize the site of leak in 50% of patients and suggested the site of the leak in 25%. Radioisotope cisternography with pledgets often gave helpful positive results when the plain films and tomography were not helpful.