Objectives: The current study investigated communicative behaviors in HR infants and infants with no family history of ASD (Low Risk; LR) at regular and frequent intervals from 8 to 24 months.

Methods: Fifty-two HR infants (23 males) and 33 LR infants (16 males) were observed at home monthly from 8 to 14 months with follow-up at 18 and 24 months. Caregivers completed the MacArthur-Bates Communicative Development Inventory (CDI; Fenson et al., 2007) at every observation. The CDI was scored according to manualized procedures (norms are based on age and gender), and two variables were analyzed: Words Produced and Words Understood. The percentages of HR versus LR infants who received scores at or below the 10^{th} percentile on each measure (considered to be an indicator of risk for communicative delay; e.g., Heilmann et al., 2005) were examined, as was the number of times infants’ scores fell below cut-off.

Results: Seventy-one percent of HR infants, as compared to 40% of LR infants, scored at or below the 10^{th} percentile on Words Produced at some point during the assessment period. Relative to LR infants, a significantly greater percentage of HR infants scored at or below cut-off at 13, 14, and 24 months, Fisher’s exact tests, *p*s < .1. Further, all LR infants falling at or below the 10^{th} percentile on Words Produced did so only once or twice; however, seven HR infants (30%) received at-risk scores three or more times. The pattern was similar for Words Understood. Seventy-five percent of HR infants versus 48% of LR infants scored at or below cut-off at least once. Compared to LR infants, the percentage of HR infants scoring below cut-off was significantly higher at 10, 11, and 14 months, Fisher’s exact tests, *p*s < .1. Additionally, while most LR infants scored at or below the 10^{th} percentile fewer than 5 times and only one LR infant reached cut-off at all seven observations, 30% of HR infants received at-risk scores six or seven times.

Conclusions: Although delays in communication development were apparent among some LR infants, there appears to be an HR subgroup that is susceptible to increased disruption in communication. Children exhibiting this profile over time may have a greater probability of showing long-term developmental problems. These findings underscore the utility of assessing HR infants’ development serially over time.