Five new sesquiterpenes (1-5) having a carbonimidic dichloride or an aldehyde function have been isolated, together with seven known related compounds (6-12), from the sponge Stylotella aurantium. The structures of the new compounds were elucidated from spectral data. The absolute stereochemistry of the previously reported reticulidin A (10) was determined. Four of the new compounds showed cytotoxicity with a range of IC(50) values of 0.1-1 microg/mL against several tumor cell lines.