Constipation is prevalent in pediatric oncology patients because of treatment with vinca alkaloids and/or narcotics and lifestyle changes secondary to disease process. Sequelae of constipation include anorexia, nausea, vomiting, abdominal pain, emergency department visits, and a decrease in quality of life. There are no reliable instruments to measure constipation in children. A pilot study (N = 21) evaluating the presence and severity of constipation and the reliability and validity of a modified version of the adult Constipation Assessment Scale (CAS) in children with cancer was conducted. Patients receiving weekly vinca alkaloids and/or narcotics = 2 times per day were recruited. Initial bowel function assessments included standardized nursing and nutrition assessments, history/physical review, and baseline CAS score repeated at 1 hour to assess test-retest reliability. Subsequent assessments included CAS administered 3 times per week and daily patient bowel diaries. Test-retest reliability was evident (r = .93; P = .000). Acceptable construct validity was indicated by a difference in mean CAS scores (t = 4.4, P <.001). Patients reported difficulty with CAS questions and response selections. Symptoms asked on CAS were often not viewed as a problem.