Limited data are available on the relationship between the strengths of test cylinders and cores taken from in-place high-strength concrete. Because high-strength concrete structures may be heavily reinforced, it can be difficult to obtain cores with the same aspect ratio (core length divided by core diameter) as cylinders. The relationship between aspect ratio and compressive strength for normal-strength concrete is well-established. But does this relationship apply to high-strength concrete? The results from five-year tests of high-strength concrete help to answer this question.