Objective: To determine the prevalence of exclusive breastfeeding (EBF) in a Basic Health Area, and the maternal factors and socio-cultural perinatal problems related to the initiation and maintenance of the EBF. Method: Observational, cross-sectional study. The study was carried out in Mazarron Health Center (Cartagena Primary Care Management, Area II, Murcia).The participants of the study were all the children born between 11/01/2004 and 11/30/2005 along with their mothers (236 children overall). The study consisted of an interview that was conducted by a nurse during the 15 months check-up. The questionnaire was made up of thirteen questions including, sex, race, place of birth, weight, birth weight, prematurity, number of siblings (Perinatal care variables), and others, such as, age, number of children, nationality, education and occupation (maternal variables) and one question on the number of EBF months. Those children who did not attend the health center and those who were not found during the data collection period did not participate in the research. Results: The number of mothers who responded to the questionnaire was 89.8% (212). The prevalence at the beginning of EBF is 75.4% (156) of all children. The average length of EBF is 2.99 months. The average maternal age is 31.26 years. The percentage of mothers who did not work was 45.9% (89). The lowest percentage of EBF is found in premature boys born by caesarean. Maternal origin positively influences EBF. The women with the greatest breastfeeding capacities are African. Conclusions: Both the prevalence at home and the average length of the EBF in the Health Area are high; the most influencing maternal factors are maternal origin and the type of childbirth. (C) 2009 Elsevier Espana, S.L. All rights reserved.