Pulsatile and steady flow fields in cerebrovascular aneurysm models of various sizes are presented in terms of laser-Doppler velocimetry measurements and flow visualization. The bifurcation angle was 140 deg and volume flow rate ratio between the branches was 3:1. The mean, peak, and minimal Reynolds numbers based on the bulk average velocity and diameter of the parent vessel were 600, 800, and 280, respectively. It is found that among the tested sizes there exists a middle range of aneurysm sizes, above and below which the forced-vortex inside the aneurysmal model is weaker and lacking, respectively, whereas in the middle range of the tested sizes the forced vortex is stronger and the fluctuation level is higher near the dome. The present results also identify the major fluid dynamic factors of the aneurysmal promotion or rupture for the medium and larger aneurysms, respectively. Furthermore, the maximum fluctuation intensity is found to increase with aneurysm size. The locations of the maximum fluctuation intensity are found to occur in the bifurcation area or at the neck instead of intra-aneurysm.