BACKGROUND. The purpose of orthodontic diagnosis and classification systems is to record different dental and arch anomalies (malocclusions). The modified Angle’s method of classifying malocclusion is still the most widely used classification system. For quantitative assessing of malocclusion different occlusal indices are used. The Eismann-Farcnik (EF) index was developed in Slovenia, but it is not routinely used in everyday orthodontic practice. AIM AND HYPOTHESIS. The aim of this study was to evaluate the validity, reliability and consumption of time in the use of the EF index, in order to assess its usefulness in everyday orthodontic practice. It was hypothesised, that the EF index was a valid and reliable method for assessing malocclusion and although being very time-consuming, it is still a good diagnostic tool for assessing malocclusion. METHODS. A set of 100 pre-treatment study casts from the patients in the permanent dentition period of (mean age of 15.4 years, SD = 0.4 year; 53 female, 47 male). Three examiners trained and calibrated in the use the EF index scored the casts. The panel of ten orthodontists individually rated the same casts for their degree of malocclusion severity. The mean rating of the panel on the severity of malocclusion was used as the gold standard for evaluating validity of the EF index. Further, the agreement of the EF index and the gold standard in assessing the severity of malocclusion was evaluated using the ICC (intra-class correlation coefficient). The ROC curve was plotted for the EF index. Ten randomly selected casts were then re-evaluated for reliability study, which was also evaluated using the ICC. Each evaluation was timed and rounded off to the nearest half of minute. RESULTS. There was an almost perfect agreement for the EF index with the decisions of the panel of orthodontists (ICC 0.819). The diagnostic accuracy, as determined by the area under the ROC curve, was found to be very good (0.846). The intra- (ICC 0.994) and inter-examiner (ICC 0.878) reliability was almost perfect. The mean time taken to assess malocclusion was 27.10 minutes. CONCLUSIONS. The EF index is a valid and reliable method for assessing malocclusion, and perfectly matches the opinion of Slovenian orthodontists. Although it is a very time-consuming method, its use for diagnostic purposes in everyday clinical orthodontic practise is still advisable.