In the Gulf of Mexico, the fishery of the oyster Crassostrea virginica is the main resource for you capture volume (42, 796 t). This resource is affected by the disease of the Dermo, which has been little studied in the Gulf of Mexico. The objective of the study was to determine the prevalence and grade of infection of Perkinsus marinus in Tabasco. Samples were realized by Fluid Thioglycolate medium (MFT), histopathology and PCR in oysters of six banks in the lagoon system Carmen-Machona-Pajonal, Tabasco. The results of the MFT after incubation, showed hipnosporas of blue-black. The histopathological analysis revealed alterations in the tissues connective and epithelial, as well as the forms characteristic of P. marinus, such as tomontes and trophozoites. The identity of the parasite was confirmed by PCR analysis. The prevalence of P. marinus registered in times of rain, north-wind and dry was 73.3, 90 and 100%; the degree of infection was 2, 3 and 5 on the scale of Mackin, respectively. There is a relationship of the prevalence and intensity of the infection with respect to increased temperature and salinity, where the dry season was most critical.