X-ray microtomography was applied for in-situ study of void coalescence during high-temperature creep of a brass alloy. Using image correlation techniques the movement of single slices and cavities connected to these images were monitored during deformation. Coalescence of voids was detected using ancestors analysis and independently checked with a geometrical parameter describing the distorted cavity shape. The analysis of in situ results suggests the existence of a critical volume fraction, as well as critical value of the ligament size between cavities at the onset of coalescence. The
maximum number of primary coalescence events takes place in the tertiary stage of creep.