Health care providers are caring for growing numbers of children with chronic illnesses and research on the effects of various interventions with these children are being increasingly published. Data from a variety of sources indicate that children with chronic illness miss more school than their healthy peers. The relative ease with which school attendance data can be obtained and analyzed and the implications of excessive school absence for children's academic performance, social adjustment, and ultimate capacity to function in society suggest that school absence rates deserve to be more broadly emphasized in research on chronic illness in childhood. Although school absence rates have not been widely used as outcome measures in such studies they do reflect a wide variety of aspects of children's health status and have been shown to be responsive to interventions with children with various physical and mental health problems. Since these rates reflect both health and non-health related factors it is important that investigators recognize the nonspecific nature of this measure and account for non-health related influences either by sampling or analytic techniques.