An outbreak of cattle abortion associated with the consumption of Hesperocyparis (Cupressus) macrocarpa and Cupressus arizonica needles has been reported in Uruguay. Twenty-five of 125 pregnant heifers in late-term pregnancy aborted after being introduced into a paddock containing numerous H. macrocarpa, C. arizonica and Casuarina cunninghamiana trees. There were no significant macroscopic or histological findings in the two fetuses analyzed. Abortifacient labdane acids were detected in the needles of H. macrocarpa (1.68%, D.W.) and C. arizonica (0.36%, D.W.) but none were found in C. cunninghamiana. •Hesperocyparis macrocarpa caused an abortion outbreak in cattle in Uruguay.•Abortifacient labdane acids were detected in needles of H. macrocarpa.•Cupressus arizonica also contains labdane acids but in small amounts.•Both trees may be an important cause of abortion in South America.