A hundred patients with multiple sclerosis and urinary disorders were examined clinically and by gas or water cystometry. Particular attention was paid to abnormalities in the voiding need sensation. These abnormalities can best be studied by cystometry combined with urethral striated sphincter electromyography. When the sequence of the three degrees of need (usual need, pressing need and urgent need) is respected, there is a good correlation between the progression of the voiding need during the filling phase of the cystometry and during the detrusor action. When there is interference with the sequence of these three degrees of the voiding need, especially the absence of the sensation normally contemporaneous with the detrusor action or immediately preceding it, there is exaggeration of either the hyperactivity or the hypoactivity of the bladder, and this aggravates vesical sensitivity: premature contraction of the detrusor muscle eliminates the first two degrees (usual need and pressing need), while progressive distension of the detrusor muscle eliminates all three stages. As the multiple sclerosis evolves a stage is reached at which there are functional mictional disorders exclusively connected with the interference with the degrees of voiding need pollakiuria and urgency.