Purpose A noninvasive method to predict the progress or treatment response of meningiomas is desirable to improve the tumor management. Studies showed that apparent diffusion coefficient (ADC) pretreatment values can predict treatment response in brain tumors. The aim of this study was to analyze changes of intratumoral ADC values in patients with meningiomas undergoing conservative or radiosurgery. Method MR images of 51 patients with diagnose of meningiomas were retrospectively reviewed. Twenty-five patients undergoing conservative or radiosurgery treatment, respectively, were included in the study. The follow-up data ranged between 1 and 10 years. Based on ROI analysis, the mean ADC values, ADC 10%min , and ADC 90%max were evaluated at different time points during follow-up. Results Baseline ADC values in between both groups were similar. The ADC mean values, ADC 10%min , and ADC 90%max within the different groups did not show any significant changes during the follow-up times in the untreated (ADC mean over 10 years period: 0.87 ± 0.05 × 10 −3 mm 2 /s) and radiosurgically treated (ADC mean over 4 years period: 1.02 ± 0.12 × 10 −3 mm 2 /s) group. However, statistically significant difference was observed when comparing the ADC mean and ADC 90%max values of untreated with radiosurgically treated ( p < 0.0001) meningiomas. Also, ADC 10%min revealed statistically significant difference between the untreated and the radiosurgery group ( p < 0.05). Conclusions ADC values in conservatively managed meningiomas remain stable during the follow-up. However, meningiomas undergoing radiosurgery reveal significant change of the mean ADC values over time, suggesting that ADC may reflect a change in the biological behavior of the tumor. These observations might suggest the value of ADC changes as an indicator of treatment response.