ABSTRACT: Numerous maternal factors may be associated with impaired lactation, including breast surgery that damages lactiferous ducts and nipple innervation, inadequate mammary glandular tissue, superimposed pregnancy, and severe maternal illness. Infants with inadequate suckling, such as prematures, small multiples, “happy to starve” nondemanding babies, or infants with oral defects may adversely affect breastmilk supply as a result of ineffective suckling. The overenthusiastic promotion of unsupplemented breastfeeding in the presence of these conditions can lead to critical failure to thrive in the infant. Case examples are cited to guide the clinician in distinguishing primary or nonremediable etiologies of insufficient lactation from common errors in the management of breastfeeding. When full lactation is not possible, the nursing relationship can still be preserved despite the need for supplement with infant formula.