Endemic to the Atlantic Forest, the southern brown howler monkey, Alouatta clamitans, can still be found in forest fragments in the metropolitan area of Porto Alegre, the capital of the state of Rio Grande do Sul, in the south of Brazil. The Urban Monkeys Program (UMP) has been monitoring their numbers since 1994. Here we report on the results of the initial surveys carried out from 1994 to 1996 and discuss the variables that are determining the loss or survival of the howler monkey groups. We also examine how our results have influenced the politics of land use over the last ten years (1997–2007). Porto Alegre has an area of 47,630 ha. About 30% is a rural/urban matrix and the remainder is entirely urban. There are 44 hills in the municipality and all have been affected by human occupation and activities. We overlaid a grid on a map 1/50,000, with quadrates of 1 km2 divided into four quadrates of 500 m2 each. We surveyed all the quadrates that contained forest. The presence of howler monkeys was recorded by direct observation, the presence of feces, and by their vocalizations. Complementary information was obtained by talking to the local people. We used a field protocol to record the absence or presence of howlers, habitat quality and the extent and type of human disturbance or use. We surveyed 5,125 ha and found howler monkeys in 2,921 ha (57%). The physiognomy, altitude and connectivity with forest in other quadrates were the three predictors of the presence of howler monkeys. Reasons for this include the fact that human use for such as agriculture, cattle breeding, housing estates, and roads is more concentrated in the lowlands than in the more hilly areas. Our findings suggest that the brown howler monkeys of Porto Alegre live as a meta-population. We participated in forums to discuss land use and management decisions. UMP influenced the creation of 895 ha of municipal protected areas over the 10 years. UMP initiated a civil enquiry concerning problems of the electrocution of howler monkeys using power lines. Two years after, as a result, the Rio Grande do Sul State Electricity Company insulated the cables in the areas where they presented a hazard. In 2002, a bill of amendment was passed (municipal law no 482/99), which provided for tax exemption for landowners who conserve natural areas or use their land for agriculture. Our recommendations for the future include: 1) maintenance of the current rural matrix in the south of Porto Alegre; 2) the creation of the “Morro São Pedro Natural Park”; 3) the establishment of a federal strategy for primate conservation in urban areas in Brazil; and 4) the inclusion of a criterion concerning human population density in the areas of occurrence for the threatened categories of the IUCN Red List.