This study tested the hypothesis that the automated assessment of a stimulated ovary, using 3D ultrasound and sono-AVC (automatic volume calculation), provides quicker analysis of follicular number and size than conventional 2D ultrasound, without any loss in measurement validity. Transvaginal ultrasound was performed on day 10 of stimulation in 89 prospectively recruited subjects undergoing IVF treatment. The number and mean diameter of follicles present in both ovaries was measured manually using 2D ultrasound. 3D data were then acquired and analysed using sono-AVC. Outcome measures included the number of follicles with a mean diameter >9 mm, >13 mm and >17 mm. The time taken for measurements and data acquisition was recorded. The two methods were compared using a paired t-test or the Wilcoxon signed rank test. Complete data were available for 82 subjects. There was no significant difference in the number of follicles with mean diameters >9 mm, >13 mm and >17 mm measured by either method. The total time taken for follicular measurements was significantly less (P < 0.01) for the automated 3D method (180.5 +/- 63.6 versus 236.1 +/- 57.1 s) which was associated with significantly less exposure to ultrasound (39.0 +/- 6.0 versus 236.10 +/- 57.1 s; P < 0.001). Automated 3D follicular measurements using sono-AVC provide a comparable but quicker assessment of follicle number and size.