As the advances in the field of cytostatic substances gain ground, more and more side effects and complications become manifest in the nervous system. Although the neurotoxic effects produced by different cytostatics present a different appearance and are partly of only sporadic or slight clinical importance, there is hardly a cytostatic which does not exercise a side effect on the nervous system. Definition of the side effects in the nervous system which are caused by cytostatics, is often difficult, because the neurotoxic syndromes are similar to disease patterns of different origin, especially those of the neoplastic and paraneoplastic type, both topically and clinico-phenomenologically. However, it is often of vital importance to arrive at the correct diagnosis well in time, because this will help the physician to decide whether the cytostatic should be discontinued or administered as before. For this reason, it may be necessary to employ, besides the neuropsychiatric examination, additional electrophysiological, CSF-diagnostic, CT and bioptic methods.