Urine marking has been neglected in prosimian primates. Captive studies showed that the Malagasy prosimian Lemur catta scent marks with urine, as well as via specialized depositions. L. catta urine mark, a multimodal signal, differs from simple urination in terms of different design features, including tail configuration: the tail is held up during marking (UT-up) and down during urination (UT-down). We explore economy and function of UT-up in the female dominant L. catta. We collected 240 h of observations on one group at Berenty (south Madagascar) during the nonmating period via all occurrences sampling. We gathered behavioral bouts/contexts (marking, traveling, feeding, resting, and fights) and recorded 191 UT-ups and 79 UT-downs. Via Global Positioning System we established the location of the places frequented i) by extragroup individuals and ii) by group members, in this case recording also behavioral context and time spent in each place. We found that L. catta UT-up is not an artifact of captivity. Moreover, UT-up in the nonmating period plays a role in territorial defense, which is mostly performed by females in L. catta society. Female UT-ups were the most investigated and UT-ups were performed/investigated more by females. Finally, signal use is parsimonious, in that urine is economically placed where and when detection probability by competitors is higher. UT-ups were performed in places most frequented by extragroup individuals and in presence of extragroup competitors (nonrandom topography and timing). In conclusion, we suggest that UT-up is an economical signal with a primarily territorial function. Am J Phys Anthropol, 2009. © 2008 Wiley-Liss, Inc.