Background: Use of complementary and alternative medicine (CAM) in children with cancer is common and probably increasing. However, data concerning differences between children and adolescents focusing on prevalence, reasons for use/non-use, costs, adverse effects, and socio-demographic factors are lacking., Procedure: A population-based survey over a 1 year period with 497 participants was conducted., Results: Of the 457 respondents (92%) 322 were children and 135 adolescents (>16 years of age) with malignancies. 31% reported CAM use from the time when being diagnosed, compared to an overall lifetime prevalence rate of 41% before cancer diagnosis. Among CAM users the most prevalent therapies were homeopathy, massage, anthroposophic medicine, acupuncture, and Bach flowers. The main reasons for use were to reduce therapy-related side effects, to strengthen the immune system, to achieve physical stabilization and to increase healing chances. Socio-demographic factors associated with CAM use were higher parental education and higher family income. A majority of CAM users (97%) would recommend CAM use. Most users (78%) informed a physician about CAM use. Side effects were rarely reported (5%), minor and self-limiting., Conclusions: The high prevalence rates seem to represent the parental or patients needs for additional treatment perceived as successful and devoid of side-effects. Clinical care and the physician-patient relation would profit from an enhanced understanding of CAM and a greater candidness towards the parental needs. Safety and efficacy - especially of CAM with high prevalence rates - should be studied in rigorous basic and clinical research., (© 2013 Wiley Periodicals, Inc.)