Background: Parent report instruments are frequently used for the identification of both "at-risk" children and to support the diagnosis of communication delay. Whilst the evidence is strong for the accuracy of parent report of vocabulary between 2 and 3 years, there are fewer studies that have considered the ability of parents to report on early communication behaviours in 12-month-old infants. Aims: To investigate the validity of the underlying structure of the Communication and Symbolic Behaviour Scales-Developmental Profile (CSBS-DP) for each of the direct observation and parent reports of communication behaviour in infants at 12 months of age. Methods & Procedures: Participants were 1725 infants, already participating in a longitudinal study of language development, whose parents completed the Infant-Toddler Checklist from the CSBS-DP. Seven hundred and twenty-eight (728) of these infants also completed the Behaviour Sample from the CSBS-DP. The structure of the CSBS-DP was examined using confirmatory factor analyses (CFA) of the Behaviour Sample and the Infant-Toddler Checklist. Correlations between the Infant-Toddler Checklist and the Behaviour Sample on the total, composite, and subscale scores were also calculated. Outcomes & Results: Confirmatory factor analysis of the CSBS-DP Behaviour Sample replicated previous work conducted during the development of the instrument, but on a larger and younger cohort of Australian infants. The data provided support for at least three factors, broadly representing Social, Speech, and Symbolic communication skills, with some evidence that the speech factor could be further split into sub-factors representing Sounds and Words. There was support for a three-factor structure for the Infant-Toddler Checklist. Moderate correlations were found between results from the Behaviour Sample and the Infant-Toddler Checklist. Conclusions & Implications: As measures of early communication skill for young infants, the CSBS-DP Behaviour Sample and the Infant-Toddler Checklist are valid clinical tools for measuring constructs broadly representing Social, Speech, and Symbolic communication skills. The Speech composite in particular emerged as a strong factor under the Behaviour Sample. (Contains 1 figure, 8 tables, and 2 notes.)