The purpose of this study was to determine symptom prevalence, characteristics, and distress in children with cancer. The Memorial Symptom Assessment Scale (MSAS) 10-18, a 30-item patient-rated instrument adapted from a previously validated adult version, provided multidimensional information about the symptoms experienced by children with cancer. This instrument was administered to 160 children with cancer aged 10-18 (45 inpatients, 115 outpatients). To confirm the instrument's reliability and validity, additional data about symptoms were collected from both the parents and the medical charts, and retesting was performed on a subgroup of inpatients. Patients could easily complete the scale in a mean of 11 minutes. The analyses supported the reliability and validity of the MSAS 10-18 subscale scores as measures of physical, psychological, and global symptom distress, respectively. Symptom prevalence ranged from 49.7% for lack of energy to 6.3% for problems with urination. The mean (+/- SD) number of symptoms per inpatient was 12.7 +/- 4.9 (range, 4-26), significantly more than the mean 6.5 +/- 5.7 (range, 0-28) symptoms per outpatient. Patients who had recently received chemotherapy had significantly more symptoms than patients who had not received chemotherapy for more than 4 months (11.6 +/- 6.0 vs. 5. 2 +/- 5.1), and those patients with solid tumors had significantly more symptoms than patients with either leukemia, lymphoma, or central nervous system malignancies (9.9 +/- 7.0 vs. 6.8 +/- 5.5 vs. 6.8 +/- 5.0 vs. 8.0 +/- 6.1). The most common symptoms (prevalence > 35%) were lack of energy, pain, drowsiness, nausea, cough, lack of appetite, and psychological symptoms (feeling sad, feeling nervous, worrying, feeling irritable). Of the symptoms with prevalence rates > 35%, those that caused high distress in more than one-third of patients were feeling sad, pain, nausea, lack of appetite, and feeling irritable. Subscale scores demonstrated large variability in symptom distress and could identify subgroups with high distress. The prevalence, characteristics, and distress associated with physical and psychological symptoms could be quantified in older children with cancer. The data confirm a high prevalence of symptoms overall and the existence of subgroups with high distress associated with one or multiple symptoms. Symptom distress is relatively higher among inpatients, children with solid tumors, and children who are undergoing antineoplastic treatment. Systematic symptom assessment may be useful in future epidemiological studies of symptoms and in clinical chemotherapeutic trials. Symptom epidemiology may also provide a focus for future clinical trials related to symptom management in children with cancer.