Service quality is a key factor in the success of a fast-food restaurant. In order for restaurant managers to know how to properly measure the level of service quality in the restaurant they manage, they must be familiar with the different models used to measure service quality. This article examines the level of service quality and guest satisfaction in fast food restaurants in the Republic of Croatia. The research was conducted in an online environment with a sample of 188 respondents. The modified SERVQUAL model was used to measure the discrepancy between expectations and perceptions of various attributes of service quality in fast food restaurants. The highest mean score for expectations and perception of the respondents was given to the reliability dimension, while the lowest score was given to the empathy dimension for expectations and perception. The highest positive discrepancy is observed for the Empathy dimension, while the highest negative discrepancy is observed for the Tangibles dimension. Research has shown that the most important to respondents was that the food was served fresh and warm, while it was least important that the restaurant staff was compassionate. The results of the empirical study can serve as a guide for all managers of fast-food restaurants on what they should focus on in improving the quality of service they provide to their guests. Furthermore, the contribution of this thesis is reflected in the fact that the analysis of previous research has identified and explained other methods of measuring service quality that can serve as a source of information for managers when they want to examine the level of service in the restaurant they manage.