Adequate documentation in medical records is important for high-quality health care. Documentation quality is widely studied within nursing, but studies are lacking within dietetic care. The aim of this study was to translate, elaborate and evaluate an audit instrument, based on the four-step Nutrition Care Process model, for documentation of dietetic care in medical records. The audit instrument includes 14 items focused on essential parts of dietetic care and the documentation's clarity and structure. Each item is to be rated 0-1 or 0-2 points, with a maximum total instrument score of 26. A detailed manual was added to facilitate the interpretation and increase the reliability of the instrument. The instrument is based on a similar tool initiated 9 years ago in the United States, which in this study was translated to Swedish and further elaborated. The translated and further elaborated instrument was named Diet-NCP-Audit. Firstly, the content validity of the Diet-NCP-Audit instrument was tested by five experienced dietitians. They rated the relevance and clarity of the included items. After a first rating, minor improvements were made. After the second rating, the Content Validity Indexes were 1.0, and the Clarity Index was 0.98. Secondly, to test the reliability, four dietitians reviewed 20 systematically collected dietetic notes independently using the audit instrument. Before the review, a calibration process was performed. A comparison of the reviews was performed, which resulted in a moderate inter-rater agreement with Krippendorff's α = 0.65-0.67. Grouping the audit results in three levels: lower, medium or higher range, a Krippendorff's α of 0.74 was considered high reliability. Also, an intra-rater reliability test-retest with a 9 weeks interval, performed by one dietitian, showed strong agreement. To conclude, the evaluated audit instrument had high content validity and moderate to high reliability and can be used in auditing documentation of dietetic care.