Families were examined at 6, 9, and 12 months in an intensive longitudinal study that included Home Behavior Attachment Q-sorts, laboratory Strange Situation assessment, home observations of infant temperament behavior on 24 occasions, observations of maternal parenting sensitivity on 12 occasions, and maternal reports of infant temperament. Maternal sensitivity was modestly related to Q-sort security and unrelated to Strange Situation classification. In contrast, observed infant temperament was more strongly related to both maternal sensitivity and Q-sort security. The relation between home and laboratory assessment of attachment security, which was at the level found in prior work (e.g., B. E. Vaughn & E. Waters, 1990), remained after the effects of observed and mother reported infant temperament were partialed. Our data highlight the need to consider other factors besides maternal sensitivity in the explanation of variability in the attachment status of 1-year-olds.