The postradiosurgical volume changes were compared with preradiosurgical growth fractions defined as the tumor doubling time and/or MIB-1 staining index in 14 patients who underwent gamma knife radiosurgery for treatment of various brain tumors. The mean preradiosurgical observation period using neuroimaging techniques was 750 days (range 80-2967 days), and the mean follow-up period after radiosurgery was 664 days (range 328-1100 days). There were four neurinomas, three meningiomas, two craniopharyngiomas, two gliomas, one hemangioblastoma, one pituitary tumor, and one intracranially infiltrative lacrimal gland tumor. The mean patient age at the time of radiosurgery was 52 years (range 8-81 yrs). There were eight males and six females. Following gamma knife radiosurgery, the mean tumor half time was estimated to be 789 days (range 124-2101 days), and the volume reduction against the preradiosurgical tumor volume ranged from 6.3% to 76.1%. This study demonstrates that gamma knife radiosurgery can control tumor growth despite the lack of a correlation with preradiosurgical tumor growth or staining indices for MIB-1. Analyses of this type are essential to show that an “unchanged tumor volume” as demonstrated by postradiosurgery follow-up neuroimaging can be regarded as showing successful radiosurgery.