Objective: To evaluate the association between perceived social support and anxiety disorders in pregnant adolescents. Methods: We conducted a cross-sectional study with a sample of 871 pregnant women aged 10 to 19 years who received prenatal care in the national public health care system in the urban area of Pelotas, state of Rio Grande do Sul, southern Brazil. We assessed perceived social support and anxiety disorders using the Medical Outcomes Study Social Support Survey and the Mini International Neuropsychiatric Interview. A self-report questionnaire was used to obtain sociodemographic information. Results: The prevalence of any anxiety disorder was 13.6%. Pregnant adolescents with an anxiety disorder reported less perceived social support in all domains (affectionate, emotional, tangible, informational, and positive social interaction). Older teenagers reported lower perceived support in the emotional, informational, and positive social interaction domains, whereas those with low socioeconomic status reported lower perceived social support in the material domain. Women who did not live with a partner had less perceived social support in the affectionate and positive social interaction domains. Conclusion: Perceived social support seems to be a protective factor against anxiety disorders in pregnant adolescents, with a positive effect on mental health.