We aimed to compare the inter-rater reliability relating to the volumetric measurement of intracranial aneurysms obtained with three-dimensional rotational angiography (3D-RA) compared with two commonly used mathematical models. Ten randomly selected aneurysms were measured by 3 independent assessors using 3D-RA and 2 mathematical models for the calculation of an ellipsoid: Equation (1), Vab = 4/3π × (a/2) × (b/2) × (a + b/4); and Equation (2), Vabc = (4/3)π × (a/2) × (b/2) × (c/2). The inter-rater reliability for each method was: 3D-RA, 0.99; Vabc, 0.90; and Vab, 0.89. The 95% confidence interval for the mean difference between 3D-RA and Vabc was not significantly different, whereas there was a significant difference between 3D-RA and Vab. Vab gave consistently higher estimates than 3D-RA. This was especially true for aneurysms with larger volumes. The use of 3D-RA to undertake volumetric measurements of intra-cranial aneurysms is both valid and reproducible for different assessors.