Parent reports have been widely used to assess child behaviours in the socio-emotional domain, but seldom have been used to assess behaviours within the cognitive domain. The present study examines the ability of parent reports and parent-administered tasks obtained through the post to assess non-verbal cognitive abilities in early childhood. In a sample of 107 2-year-olds, age-corrected scores on parent reports and parent-administered tasks assessing non-verbal reasoning significantly predicted performance on the Mental Development Index (MDI) of the Bayley Scales of Infant Development-II two weeks later (r = .49 and r = .41, p < .0001, respectively). The multiple correlation between the two components and the MDI was .55 (p < .0001). This ability of parental assessments to predict the MDI is comparable to the predictive power of standard tester-administered measures at this age, even though the parent measure specifically excludes verbal items that are included in the MDI. Adding parent reports of language development significantly improved the prediction of the MDI (R = .66, p < .0001). In addition, higher within-domain than cross-domain correlations reflect a significant ability of parents to discriminate verbal and nonverbal abilities.