BACKGROUND: The use of CAM by the relapsed pediatric oncology population has largely gone unstudied. The main objective of this study was to describe the prevalence of and change in CAM use in oncology patients for whom frontline therapy had failed. Secondary objectives included describing patient/family objectives for using CAM, satisfaction with CAM, financial and time expenditures on CAM, and patient desire for physician involvement in CAM use. PROCEDURE: Fifty-four patients 0-25 years of age, for whom frontline therapy had failed, were enrolled. The subjects completed an anonymous one-time self-administered questionnaire. RESULTS: Eighty-two percent of respondents reported using CAM, 52% of which reported initiating or increasing CAM use after failure of frontline therapy. The most commonly used CAM categories were prayer/spiritual healing (83%) and oral/dietary supplements (31%). Prayer/spiritual healing was most commonly used to cure or slow the progression of cancer (59%). Oral/dietary supplements were used to improve overall health and well-being (65%). Estimates of money and time spent ranged from $0 to >$1,275 (median $225) and 1 to > 700 hr (median 10 hr). Sixty percent of CAM users reported their oncologist was unaware of their use. Most participants who used non-spiritual/prayer CAM continued use while hospitalized or while receiving chemotherapy. CONCLUSIONS: Understanding usage patterns may better help pediatric oncologists and palliative-care specialists address the needs of this population, and protect against potentially dangerous drug interactions or side effects from combined CAM and chemotherapy use.