Cerebrospinal fluid (CSF) pressure was measured in four groups of patients: 116 with acute pseudotumor cerebri, 18 with chronic pseudotumor cerebri, 41 obese and 15 nonobese normal patients undergoing spinal anesthesia. Spinal fluid pressure between 200 and 250 mm H2O was found in members of each group. This suggests that when elevated CSF pressure is suspected, confirmation requires values greater than 250 mm H2O. The CSF pressure and degree of obesity could not be correlated in any meaningful way. There was no significant statistical difference between the mean CSF pressures obtained in the obese and nonobese normal populations.