Assessment of nutritional status in children with cancer is important but measures based on weight can be problematic at diagnosis, especially in those with advanced disease. Likewise, dual energy x-ray absorptiometry may be confounded by other radiological procedures and is not commonly available in low-income countries where most children with cancer live. Arm anthropometry is not subject to these constraints. In a study sample of 99 Canadian patients with cancer at diagnosis, mid-upper arm circumference correlated well with lean body mass as measured by dual energy x-ray absorptiometry but triceps skin fold thickness was a poor predictor of fat mass. Arm anthropometry can be a useful tool for the measurement of nutritional status in children with cancer. However, further studies, particularly in low-income countries and in children with solid tumors at diagnosis, are required to determine the full extent of its utility.