We have assessed the clinical growth index as an indicator of tumour growth rate in 50 patients with a vestibular schwannoma. Clinical growth index was calculated by measuring the length of history and dividing it by the maximum tumour diameter. Total tumour volumes were also measured from all MRI examinations and an effective tumour volume doubling time was calculated. Radiological growth measurements demonstrated involution in 10/50 patients. The median volume doubling time was 1.65 years (range 20.9-46.3 months, skewness 1.72 years). The median clinical growth index was 0.030 cm per month (range 0-0.270 cm per month, skewness 2.398). There was no significant correlation between volume doubling time and clinical growth index. Identification of rapidly growing tumours with clinical growth index >0.025 cm/month had a positive predictive value of 61%, negative predictive value of 48%, false-positive rate of 30% and false-negative rate of 52%. In conclusion, we have shown that the growth rate of vestibular schwannoma is not related to the clinical growth index and we recommend that this measure should be abandoned in the clinical management of patients where conservative management regimes are being considered.