The American Society of Clinical Oncology (ASCO) published updated practice guidelines in the April 2 issue of the Journal of Clinical Oncology (J Clin Oncol) that recommend adjusting chemotherapy drug doses to the actual weight of obese cancer patients. There is no evidence that full weight-based chemotherapy dosing produces greater toxicity than corrected dosing, and concerns about overdose in obese cancer patients are unfounded. A systematic review showed that many overweight or obese patients continue to receive low doses of cytotoxic drugs because of high uncertainty among clinicians regarding the optimal drug dose, although studies have demonstrated that complete weight-based chemotherapy dosing is safe and critical for patient survival. Many oncologists continue to calculate body surface area based on ideal weight or corrected ideal weight rather than actual weight, which results in large variability in chemotherapy doses for overweight and obese patients, and up to 40% of chemotherapy doses are lower than the ideal dose. The ASCO guideline panel evaluated all relevant randomized clinical trials, meta-analyses, and clinical practice guidelines and made the following key recommendations in the updated guideline: (1) actual body weight should be used to select chemotherapy doses for cytotoxic agents regardless of obesity; (2) the same dose reduction strategy should be used for obese patients as for other patients, taking into account the type and severity of toxicity, co-morbidities, and therapeutic goals. (3) Fixed doses should be considered only for selective cytotoxic agents for which maximum dose limits have been established; (4) Any of the currently available standard formulas can be used for calculation of body surface area, and there is no evidence that one formula is superior to the others; (5) More in-depth studies on the pharmacokinetics and pharmacogenetics of chemotherapeutic drug dosages for obese patients are needed in the future. The guidelines also emphasize the need for clinicians to conduct more in-depth studies on this issue. The guidelines also emphasize the need for clinicians to discuss this issue in detail with patients and caregivers, and highlight the need for higher doses in obese patients to ensure that chemotherapy is effective and that proportionally higher doses do not produce greater toxic effects. The guideline does not address these classes of drugs because of the lack of literature on the dosing of newer drugs such as tyrosine kinase inhibitors and monoclonal antibodies.