The development of a varicella vaccine has raised questions about the cost effectiveness of vaccination, but little information on the costs of chickenpox exists. The purpose of this study was to evaluate medical costs and the value of work loss among families whose children had chickenpox. Interviews were conducted with 179 families who made advice nurse calls or urgent care clinic visits to three clinics in the Northern California Kaiser Permanente Medical Care Plan. Two-thirds of working mothers and one-third of working fathers missed work to care for children with chickenpox. The mean value of the work lost because of chickenpox was $293/family or $183/chickenpox case. The estimated costs of nonprescription medications were $20/family or $12.50/chickenpox case. Children were sick enough to need to stay home for only one-third as many days as chicken actually stayed home because of school exclusion policies. These empiric results differ from previous estimates of the medical and work loss costs of varicella and should be included in analyses of the cost effectiveness of proposed vaccination programs.