Little is known about the psychosocial process of parental decisions on 'drop out' from cancer treatment for paediatric patients in Taiwan. This study, based on structured in-depth interviews, attempted to document the determinants of parental decisions on drop out. A total of 19 parents of paediatric cancer patients who dropped out from a cancer treatment for at least a month within 3 years since first treatment were interviewed. Content analysis of qualitative data revealed six categories of determinants associated with parental decisions: suffering severe pain from medical treatments and adverse side-effects; desire for better and less painful treatments; adverse effect of other patients' experiences; searching for possible explanations for disease after prolonged denial of diagnosis; lack of empathy from health care professionals; and misinterpretation of improved prognostics. These findings reflected the deficiency of psychological and emotional support for parents from health care professionals prior to and during cancer treatment.