Colonies of Montastraea cavernosa were exposed to daily applications of approx. 200–225 mg cm– 2 sediments, during a four-week period, in order to investigate coral responses to increased sedimentation. Effects were assessed based on the histopathological condition of specimen tissues. Mild stress responses were noted as early as week one, including tissue swelling and polyp retraction, as well as changes in size and appearance of mucous secretory cells. As stress progressed, further inflammation of the mucous secretory cells was observed. Severe effects were observed in weeks 3 and 4, including atrophy of the outer epidermis, increased granularity and debris in gastrodermal cells of the middle and lower polyp region, as well as swelling and granularity of the calicoblastic epithelium. A semiquantitative rating scale was developed to score tissue condition based on the histopathological changes observed in control and treated corals. Although some signs of stress were also present in some control colonies, statistical analyses indicated significant differences in histopathological condition between control and treated corals. Our results confirm previous research that sublethal effects of sedimentation on corals are complex, involving both localized and systemic cell injury. Our results offer insight with regards to the diagnosis of healthy vs. unhealthy condition in reef corals, and provide a framework to survey for cellular reactions to environmental stress in coral reefs.