The aim of the paper is to compare the quality of nursing documentation in the Children's Hospital before and after the NANDA-I nursing diagnoses training. Research employed the interventional study design, and pre-post study design. Before and after the NANDA-I nursing diagnoses training, 50 nursing records were analyzed in the interventional pre-post study, using D-Catch instrument. The most often documented problem-centered nursing diagnosis before training was anxiety and after the training, hyperthermia. The most common risk diagnoses before and after the training was risk of infection. Before the training, one health promotion diagnosis was determined in the nursing records, and after the training the number increased to four. The highest value was given to readability of the nursing documentation both before and after the training. The lowest score before the training was given to the quality determiners of the accurate nursing diagnoses and after the training given to the determiners of the results' quantity. The sum score of documenting the nursing interventions was the most inconsistent before the training and after the training. The most consistent was the readability of the nursing records before and after the training. Statistically significant differences in the improvement of quality were revealed in all areas except for the readability of the nursing documentation and the quantity of nursing assessment. The results of the study revealed that following the training, the quality of nursing documentation improved, the wording of the nursing diagnoses improved, and the number of accurate nursing diagnoses had increased. Results of the research provide an overview of the importance of the training in improving the quality of nursing documentation and aid the educators in planning the trainings, focusing more on the challenges in the documentation.