In the Neurosurgery Department, Silesian University School of Medicine, continuous monitoring of selected neurophysiological functions of the central and peripheral nervous system was introduced in 1998 as a routine procedure in cerebellopontine angle surgery and some other operations performed in the petroclival region. Such benefits from this method as increased patient safety, availability of information about dynamic changes in the monitored structures, and the possibility of cranial nerves localization using stimulation in the operating area, are quite obvious. The paper presents results of a detailed statistical analysis of the amount of time required for preparation and for operating in 174 cerebellopontine angle tumor surgeries performed in the years 1986-2002 with (group M) and without (group BM, before the year 1998) intraoperative monitoring. Subgroups distinguished according to the histological type of tumor were evaluated. Out of 95 procedures performed in group M, 57 were operations of acoustic neurinoma cases, 15 meningiomas, 8 cases of epidermal cyst, and 15 other growth processes in the cerebellopontine angle region. Among 79 operations in group BM, there were 57 cases of acoustic neurinoma, 4 cases of meningioma, 8 cases of epidermal cyst, and 10 of other types of neoplastic growth. In group M as compared to group BM the pre-op. preparation time was found to be significantly longer in cases of the VIII-th nerve neurinoma, and of other tumors. No statistically significant differences in the amount of operating time in were found between any of the subgroups. Both radicality of tumor removal and facial nerve status have clearly improved since intraoperative monitoring was introduced.