The early development of SIB in young children with developmental disabilities was examined by tracking over an 18-month period 16 school-age children who had recently started to show early SIB. Naturalistic observations were conducted in each child's classroom every 3 months, and the association between early SIB and environmental events was examined. Results showed that for the 4 children whose early SIB had escalated over this period, there was a significant association between early SIB and low levels of social contact across observation points, supporting models of the development of SIB. This association might be considered as a risk marker for the exacerbation of SIB. Implications of this finding for targeting early interventions for SIB are discussed.