How many infants, toddlers, and preschoolers with disabilities potentially could be served under the Individuals with Disabilities Education Act (IDEA)? New estimates from the U.S. Census Bureau's Survey of Income and Program Participation (SIPP) suggest that there were as many as 851,000 children with disabilities, birth to 5, during the 1991-1992 school year. The SIPP figures indicate that 80% of these children had received developmental services. The SIPP data also show that many children were served privately, rather than through IDEA or Chapter 1 of the Elementary and Secondary Education Act. Information in the SIPP also demonstrates the need to conduct outreach to low socioeconomic status (SES) and minority families with children under age 6 years.