Lafoensia pacari (Lythraceae), popularly known in Brazil as "pacari", is a small tree native to the Cerrado that is used in folk medicine to treat cancer and as an anti-inflammatory and cicatrizing agent. We evaluated the genotoxic, cytotoxic, antigenotoxic, and anticytotoxic activities of an ethanol extract of L. pacari stem bark (EESB) using the Ames test and the mouse bone marrow micronucleus test. In the Ames test, EESB did not significantly increase the number of His(+) revertants in Salmonella typhimurium tester strains TA98 and TA100 at all doses, demonstrating lack of mutagenicity. Only the highest dose of EESB significantly increased the micronucleated polychromatic erythrocyte frequency in the micronucleus test, indicating mild genotoxicity. EESB produced a mutagenic index lower than the negative control in the Ames test. In the micronucleus test, at all doses, EESB caused a significant decrease in the polychromatic/normochromatic erythrocyte ratio (PCE/NCE) at 24 h compared with the negative control. EESB co-administered together with the respective positive control caused a significant decrease in the number of His(+) revertant colonies in the Ames test and in the frequency of micronucleated polychromatic erythrocytes in the micronucleus test, demonstrating a DNA protector effect. EESB co-administered with mitomycin C significantly increased the PCE/NCE ratio at all doses, showing an anticytotoxic effect. We conclude that EESB has antigenotoxic and anticytotoxic properties.