Dr. Moewardi Hospital is a teaching hospital that has been accredited by KARS. Carcinoma mammae was in the first place in the top 10 inpatient diseases. The purpose of this study was to determine the relationship between the completeness of medical information with the accuracy of the diagnosis code of carcinoma mammae on inpatient medical record documents. This method of research is observational analytic and uses a cross sectional approach. The population of this study was 757 inpatient medical record documents. Number of sample was 90 with used Simple Random Sampling technique. Percentage of the accuracy diagnosis code as many as 14 (15.56%) documents while inaccurate code 76 (84.44%) documents. Completeness of medical information from the 90 medical record documents studied there were 61 (67.78%) documents with complete categories and 29 (32.22%) documents with incomplete categories. Based on the results of statistical tests, the significance value was 0.347, so 0.347> 0.05. That is, the completeness of medical information does not have a significant relationship with the accuracy of the diagnosis code of Carcinoma mammae. As for the calculation results, the odds ratio is 0.524, the figure shows that complete medical information has the opportunity to obtain a diagnosis code that is more accurate 0.524 times when compared to incomplete medical information.