Background: Standardized forms for prescription and medication administration are one solution to reduce medication errors in the chemotherapy process. Gastric cancer is the most common cancer in Iran. In this study, we have attempted to design and validate a standard printed chemotherapy form and evaluate adherence by oncologists and nurses to this form.Methods: We performed this cross-sectional study in a Mashhad, Iran teaching hospital from August 2015 until January 2016. A clinical pharmacist designed the chemotherapy form that included various demographic and clinical parameters and approved chemotherapy regimens for gastric cancer. Clinical oncologists that worked in this center validated the form. We included all eligible patients. A pharmacy student identified adherence by the oncologists and nurses to this form and probable medication errors. Results are mean ± standard deviation or number (percentages) for nominal variables. Data analysis was performed using the SPSS 16.0 statistical package.Results: We evaluated 54 patients and a total of 249 chemotherapy courses. In 146 (58.63%) chemotherapy sessions, the administered regimens lacked compatibility with the standard form. Approximately 66% of recorded errors occurred in the prescription phase and the remainder during the administration phase. The most common errors included improper dose (61%) and wrong infusion time (34%). We observed that 37 dose calculation errors occurred in 32 chemotherapy sessions.Conclusions: In general, adherence by oncologists and nurses with the developed form for chemotherapy treatment of gastric cancer was not acceptable. These findings indicated the necessity for a standardized order sheet to simplify the chemotherapy process for the clinicians, and reduce prescription and administration errors.