The study aimed to identify, in a Rooming-in unit, diagnoses related to the phenomenon of breastfeeding according to the NANDA-I Taxonomy II. It was conducted a descriptive exploratory study involving 83 mothers and their babies in the period of February to April 2011. Data were collected by means of an instrument based on the Theory of Basic Human Needs and, after statistical analysis, presented in tables. The results showed that the most frequent nursing diagnosis was Effective breastfeeding, identified in 65 (78.3%) cases. It is estimated that the nursing diagnoses related to breastfeeding can contribute to nursing care so that it can be more targeted, in order to promote a more qualified, effective and human care.