Background Arm anthropometry is a better indicator of nutritional status in children with cancer. The value of serum albumin and prealbumin in nutritional assesment is debatable. We investigated the nutritional status of children with cancer and their serum albumin and prealbumin levels. Patients and Methods At diagnosis and following induction therapies, weight, height, body mass index (BMI), mid-upper arm circumference (MUAC), and triceps skin-fold thickness (TSFT) were measured; serum albumin and prealbumin levels were determined. Prevalences of malnutrition defined by anthropometric indices were calculated. Correlations of anthropometric indices with each other, with serum albumin/prealbumin levels, and clinicopathological parameters were analyzed. Results In 81 patients, median age was 7.5 years (males/females = 50/31), tumors were located mostly in the abdomen, and abdominal tumors were more common under 5 years. Prevalence of malnutrition according to weight for age, BMI, MUAC, TSFTzscores were 14.8%, 23.5%, 27.2%, 21%, respectively. Defined by combined BMI/MUAC/TSFT measurements, 33/81 cases (40.7%) had malnutrition (zscores < -1, 23 mild;zscores < -2, 10 moderate). Malnutrition was more prevalent under 5 years (P = .03), also in abdominal tumors (P = .03) and advanced disease (P < .001). Younger age and advanced disease were risk factors for malnutrition. At diagnosis, prevalences of low serum albumin and prealbumin levels were 7.4% and 54%, respectively. Cases with malnutrition had significantly lower survival rates. Conclusions Nutritional status is assessed best by MUAC and TSFT measurements. Serum prealbumin levels can be used to identify patients at risk of undernutrition. Presence of malnutrition is a significant poor prognostic factor. All children with cancer should undergo nutritional evaluation and active nutritional support.