Closed (occult) spinal dysraphism, e.g. lipomyelomeningocele, intraspinal lipoma, diastematomyelia, the tethered spinal cord in its various forms and dysgenesis of the sacrum, is often diagnosed late and only symptoms of neurogenic bladder dysfunction are present. A lipomyelomeningocele mostly causes detrusor and sphincter dysfunction, as was the case in five of six children among our patients. However, improvement of neurological and urological symptoms after the operation can only be achieved in about 40%. Four of eight children with diastematomyelia suffered from neurogenic bladder dysfunction; three have meanwhile undergone surgery with complete recovery in one, no relevant change in the second, and worsening in the third. Originally a specific term, the "tethered spinal cord" when associated with spinal dysraphism has taken on a more general meaning. Nowadays this term is not only used for a short, thickened and tight filum terminale, but comprises any pathology, which prevents the spinal cord from ascending. MRI examination of the craniovertebral junction and spinal cord of patients with treated myelomeningocele often reveals secondary pathologic changes: these may be areas of cord atrophy, hydromyelic cavitation or ventral compression from arachnoid cysts with clinical symptoms mostly after the age of 5 years. In these children a changing urodynamic pattern may therefore be caused by such a pathology and is an indication for a thorough neurological examination including MRI. Of all the dysrhaphic states mentioned above, sacral dysgenesis is the most frequent. The sacral osteological anomaly, as a numerical and as a structural anomaly, also determines the neuro-urological deficit.(ABSTRACT TRUNCATED AT 250 WORDS)