The three objectives of this longitudinal study were to examine temperamental perceptual sensitivity (IBQ-R; Gartstein & Rothbart, 2003) as a predictor of cognitive growth at 20 months, attachment style (Strange Situation; Ainsworth et al., 1978) as a predictor of infant cognitive growth (Mental Development Index scores; Bayley, 1993) at 20 months, and the moderating effect of attachment x perceptual sensitivity on cognitive growth at 20 months. Two latent basis models with mother-infant attachment security, and father-infant attachment security, respectively, were used to address the research questions. The relationship between attachment security and cognitive outcomes is established but understudied. Attachment security is associated with academic achievement, language competence, developed vocabularies in children (i.e. van IJzendoorn et al., 1995; Sroufe, 2005; Pallini et al., 2014), yet there is very little research on cognitive outcomes in infancy or toddlerhood (i.e. Ding, 2014). Virtually no research exists on the relationship between perceptual sensitivity and cognitive outcomes. Latent basis growth curve models revealed that attachment security with mothers was a significant predictor of MDI scores in infants at age 20 months. Temperamental perceptual sensitivity significantly predicted MDI scores in infants at age 20 months in the mother-infant attachment model. The father-infant attachment model revealed non-significant results. An exploratory aim of this study was to discern differences between the results of the mother-infant attachment model, and the father-infant attachment model, which were present. Therefore, this study also adds to the literature distinguishing father-infant attachment from mother-infant attachment.