Patterns of attachment in preschool-age children were investigated in a nonexperimental, naturally occurring stressful situation. The sample included 86 families with at least one child 18 to 54 months of age. In each family, the mother planned to deliver another child in a hospital birthing center. Separation from the mother during admission was found to elicit a stress response from the child. When the child was reunited with the mother, a detailed description of the child's behavior was recorded and scored on Ainsworth's four interactive behavior rating scales. An attachment pattern was then determined. A total of 49 children were categorized as securely attached, 4 as resistant, and 33 as avoidant. The relative proportions of securely attached and anxiously attached preschoolers were similar to those reported in most studies of middle class American children. However, a much higher than usual proportion of avoidant responses was found among the anxiously attached, suggesting that anxiously attached children may be particularly vulnerable to the high stress associated with sibling birth. The child's behaviors toward the newborn were observed; securely attached children were consistently more positive in their responses than those seen as less securely attached. The data supported the premise that attachment patterns can be validly assessed in a naturally occurring strange situation involving preschool children. (Author/RH)