Introduction: Quality control of viewing boxes consists of measurements of viewing box brightness, viewing box brightness uniformity and ambient lighting levels in radiographer viewing areas. WHO (1992), CEC (1997, according to McCarthy in Brennan, 2003), NORDIC (1999) and IPEM (2005) recommendations determine the acceptable levels of the above mentioned parameters. Purpose: The purpose of this article was to measure the brightness and brightness uniformity of viewing boxes and ambient lighting levels in three Slovenian hospitals and to compare the results with the international recommendations. Methods: Three major Slovenian hospitals were included in this study. The parameters were acquired on 37 viewing boxes in radiographer viewing areas. An appropriate calibrated meter Light-O-Meter was used for the measurements and a recommended equation was used to calculate brightness uniformity. Results and discussion: 51 % of the viewing boxes met the minimum standards of the average viewing box brightness, 72 % of the viewing boxes met the minimum standards for brightness uniformity and 76 % of radiographer viewing areas met the criteria for the ambient lighting level. Conclusion: This study showed that the measured parameters of viewing boxes included in this article were better than the results from other studies and for that the measures to improve the functioning of viewing boxes were suggested. It is necessary to include the quality control of viewing boxes in the quality control programme at the diagnostic radiology department.