The aim of this study was to evaluate the type of microbiota present in root canals with pulp necrosis, with and without periapical lesion. Nineteen patients were selected for the study and 30 root canals were analysed in unirradicular and/or multi-radicular permanent teeth, asymptomatic, with pulp necrosis, with or without periapical lesion, and no communication between root canal and oral cavity. Absorbent paper cones were introduced in the canal for 20 s. Then, the contaminated paper cones were inoculated in a Brain Heart Infusion Agar-BHI culture medium and incubated in an oven for 48 h at 37°C. The data were analysed by non-parametric statistical method of the Cochran-test. The results revealed that there was no statistically significant difference between the amount of Gram-positive and negative bacteria in endodontic infections, indicating that the microbiota of these endodontic infections is mixed.