Knowledge of blood parasites in Brazilian chelonians is limited, since they have been recorded in only six species. Mesoclemmys vanderhaegei (Bour) is a freshwater turtle with a wide geographic distribution in Brazil, but there is little information about its natural history. This paper reports on a study of the prevalence and infection intensity of a haemogregarine in two subpopulations of M. vanderhaegei. The study was conducted in two areas of Cerrado in the Upper Paraguay River basin in the state of Mato Grosso, Brazil, between November 2010 and August 2013. Ninety-five (53%) of the 179 turtles captured were positive for haemogregarine parasites. The parasitic forms observed were two morphotypes of intraerythrocytic gametocytes. The prevalence differed between size classes, increasing significantly according to the animals' body size. There was no significant difference between prevalence and sex, or between sampling periods. The mean parasite intensity was 9 parasites/2,000 erythrocytes (0.45%) and the parasite population presented an aggregated distribution, with an aggregation index of 19 and discrepancy of 0.772. This is the first record of a hemoparasite in the freshwater turtle M. vanderhaegei., Vinícius C. Goes, Elizângela S. Brito, Rafael M. Valadão, Camila O. Gutierrez, Amanda M. Picelli, Lúcio A. Viana., and Obsahuje bibliografii