On this occasion we look back on 25 years of the Deutsche Gesellschaft fur Neuro chirurgie. They hold a great deal: founding and development of the society, comple tion and extension, communication between the individual members and contacts to other societies beyond our borders. They also stand for close co-operation with those who transfer their patients to u- the neurologists and specialists in internal medicine, the ophthalmologists and ear nose-and throat specialists as well as the general surgeons. This 25th annual meeting will deal with two examples of diseases that present common problems to the neurologist and to the neurosurgeon, namely meningiomas and multiple sclerosis. In view of their long histories often going back over many years, both of these lesions lead to diagnostic errors and indequate treatment. And yet it should be possible to recognize meningiomas at an early date and to initiate the only possible treatment, the operation,if all diagnostic measures are repeatedly carried out. The diagnosis MS, on the other hand, with the multiplicity of symptoms which are peculiar to this disease, should continue to be re-examined until every other lesion has been excluded with certainty. The increasing number of legal proceedings because of diagnostic and therapeutic measures as well as the doctor-patient talk preceding the written consent for these measures are further problems in need of discussion. For this reason, the topic "medical liability in special reference to the neurosurgeon" was chosen for this meeting. Many questions necessitate many answers.