According to data from the National Health Interview Survey (NHIS) over two million children under 17 years (3.8%) are afflicted by chronic conditions that cause some limitation of activity. The limitations range from complete inability to attend school for school age children or inability to engage in play for preschoolers to limited ability to engage in athletics or other social activities. Analysis of micro data from the NHIS reveals that the leading causes of activity limitation include: respiratory diseases; speech, special sense and intelligence related impairments; and mental and nervous system disorders. Together these conditions account for 50% of all childhood activity limitations. Despite their small numbers, children with activity limitations are reported by the NHIS to consume a disproportionate share of health care resources, including over twice as many physician services and over seven times as many hospital services as other children. Household interviews appear to be a useful vehicle for assessing prevalence of activity limitations but researchers and others should be cautioned about the subjective nature of the activity limitation concept.