Popcorn disease, known to be caused by Ciboria carunculoides (Siegler and Jenkins) Whetzel, was observed on a single white mulberry tree (Morus alba L.) growing in south central Kentucky. The disease was not found on other white or red (Morus rubra L.) mulberries growing nearby. Diseased fruits were significantly (P<0.01) heavier, longer, and wider than normal fruits. On the lower branches, approximately one-half of the berries were diseased, whereas the proportion of diseased fruits decreased in the higher branches.