Few studies have attempted to describe the experience of symptoms in young children with cancer. This is due, in part, to the lack of validated symptom assessment scales for this patient population. The objective of this study was to evaluate the reliability and validity of a revised Memorial Symptom Assessment Scale (MSAS) in patients aged 7-12 as an instrument for the assessment of symptoms in young children with cancer. The MSAS (7-12) was administered to 149 children (inpatients and outpatients) who were undergoing treatment at either the Royal Marsden NHS Trust, London, United Kingdom or The Children's Hospital at Westmead, Sydney, Australia. Validity was evaluated by comparison with the medical record, parental report, and concurrent assessment on visual analogue scales for selected symptoms. The data provide evidence of the reliability and validity of MSAS (7-12) and demonstrate that children with cancer as young as 7 years can report clinically relevant and consistent information about their symptom experience. Young children with cancer experience multiple symptoms. Approximately one-third had experienced lethargy and/or pain and/or insomnia during the 48 hours prior to the completion of MSAS (7-12). The completion rate for MSAS (7-12) was high and the majority of children completed the instrument in a short period of time and with little difficulty. The instrument appears to be age appropriate and may be helpful to older children unable to independently complete MSAS (10-18). Systematic symptom assessment may be useful in future epidemiological studies of symptoms and in cancer chemotherapy drug trials.