A consecutive series of 143 unselected adult patients with histologically proved World Health Organization grade II gliomas was reviewed to assess the prognostic value of growth rates of mean tumor diameters on successive magnetic resonance images before treatment. There is an inverse correlation between growth rates and survival (p < 0.001; median survival at 5.16 years for a growth rate of 8mm/year or more; median survival >15.0 years for a growth rate <8mm/year). Thus, individual magnetic resonance imaging tumor growth rates should be incorporated in the planning of the initial therapeutic strategy of grade II gliomas.