In Mexico, people with limited resources who seek specialized attention in mental health generally go to primary health care, where their first contact is with social workers. There is little information about the activities of social workers in the field of mental health, and little recognition of their role. The aim of this study is to characterize the role of the social workers in health centers in Mexico City. We used an exploratory sequential mixed methods design (QUAL -> quan) in two phases. The first phase consisted of interviews with 15 social workers, and the second a survey of 92. The qualitative information was analyzed through the establishment of categories and subcategories, and the quantitative data using descriptive statistics. The results of the two phases were then triangulated. The majority of the social workers had specialized diplomas from technical high schools, with little training in mental health. They identified two types of patients, those with mental illness and those with emotional problems; the latter were the most common patients in the health centers. Patients with mental illness were given information and referred to specialists; those with emotional problems were given orientation, counseling, and referrals, and above all, they were listened to. We believe that these activities are important: given the shortage of specialists, they offer patients a space for catharsis, for venting their emotions. Social workers receive little recognition for this labor, a fact related to an institutional reproduction of medical authority that does not take into account the social view of illness.