We have studied the concentration distribution of microbubbles in forced isotropic turbulence. An initially uniform concentration field is shown to evolve to a highlyintermittent orspotty concentration distribution at long time due to the interactions of microbubbles with small-scale, intense, and coherent flow vortical structures. The maximum bubble concentration can be as large as 3,000 times the mean concentration and the local accumulations occur preferentially in the regions of high flow vorticity and low flow pressure. A quantitative measure of global nonuniformity in the concentration field is used to confirm that the preferential accumulation does follow Kolmogorov scaling, as opposed to the large-scale scaling commonly used for dispersion quantification.