Ecological and behavioral plasticity allow marmosets, genus Callithrix, to adapt and succeed in urban areas. This research assess proximity and relationships between Wied's marmoset Callithrix kuhlii, domestic animals and residents of Ilhéus, Bahia, Brazil. We collected data on the species' urban ecology and biology, since it has been little studied so far. Tools for data gathering included semi-structured interviews, direct observations and GPS-mapping. There were sightings within the three major districts of Ilhéus, with 37% of positive questionnaires (n = 359) for marmoset sighting at least weekly. Therefore, marmosets were considered common in this city. Most records and frequent sightings were associated with secondary forest fragments, backyards with fruit trees and mangroves. Marmosets travel among urban fragments using electrical and phone wires and crossing roads. There is a relatively small number of accidents when compared to the number of sightings, with electrocution as the most common. Visitation of marmosets to households, attracted by food provisioning, was considered frequent. People feel pity for the marmosets and lure them to their houses through food, but offered items are not always suitable. Marmoset exploration of uncommon habitats, such as mangroves, might be driven by a lack of larger forest fragments within the city.