Carbon dioxide urethral pressure profiles were analyzed under the same conditions for 113 spina bifida and 87 non-spina bifida patients categorized by sex and age. Either duplicate or triplicate measurements were obtained from each patient for parameters of continence length, closure pressure and functional length. The degree of reproducibility of each parameter varied depending on age, sex and diagnosis. Except for 1 age-sex category closure pressure exhibited the smallest degree of relative variation for spina bifida patients. Results for non-spina bifida patients were mixed in that the measurement of no one parameter resulted in a uniformly smallest degree of relative variation. Reproducibility based on within patient variability generally was least for the continence length.