Identification of early signs of Autism Spectrum Disorder (ASD) could lead to earlier diagnosis and intervention. This cross-sectional study used the Parent Observation of Early Markers Scale (POEMS, Feldman et al. in J Autism Dev Disord 42:13-12, 2012) to identify early signs of ASD in 69 ASD high-risk (older sibling diagnosed with ASD) and 69 sex and aged-matched ASD low-risk second-born or later infants (no family history of ASD) between 6 and 36 months of age. Family sociodemographic comparisons were also made between the risk groups. The high-risk children had significantly more elevated POEMS items than the low-risk children at 12, 18, 24, 30 and 36 months of age, even when the children subsequently diagnosed with ASD were removed from the analyses. Families of the high-risk group had older parents, lower family income and fewer mothers working out of the home than the low-risk group. These sociodemographic variables were not significantly correlated with POEMS scores. The results suggest that high-risk infants may show signs of the broader ASD phenotype as early as 12 months of age that may be unrelated to observed sociodemographic family differences.