Blood films and selected tissue sections from 270 gray squirrels (Sciurus carolinensis) from 18 sites in 11 southeastern states were examined for Hepatozoan griseisciuri. This parasite was found in 110 (41%) squirrels from 17 of the 18 sites. Data suggested transmission of the parasite apparently occurs throughout the year and increases from spring to late summer. The infection was more prevalent in subadults and adults than in juveniles. Schizogonic stages were found only in the lungs, suggesting this organ is a major site of schizogony. Pathologic changes associated with H. griseisciuri infection were thickening of alveolar walls, eosinophil infiltration, pulmonary congestion and atelectasis.