In this study, we analyzed the intensities and frequencies of short-term heavy rainfall using extreme indices based on sub-daily rainfall values with durations of 1, 3, and 6 hours. The analysis was conducted using hourly data from rain gauges in the DHMZ network across Croatia for the period from 1961 to 2020. It includes basic climatology of monthly, seasonal, and annual sub-daily rainfall maxima. The results indicate that the highest intensities and frequencies of sub-daily rainfall extremes in Croatia occur in the northern and southern Adriatic regions and Gorski kotar. The timing of peak intensity and frequency of extreme events both occur in the same season for each region, suggesting that these aspects are influenced by similar processes linked to the peak of convective and thunderstorm activity. On the mainland, maximum sub-daily rainfall is observed during the summer, while in mountainous areas and along the Adriatic coast, it is noticed somewhat later, towards the end of summer and the beginning of autumn. Significant contributions to daily rainfall from sub-daily extremes were also observed on the mainland, indicating that these events may result from either isolated short-duration events or are part of longer storms with pronounced peaks. The analysis reveals that the timing of the wettest hour predominantly occurs around midnight. However, in the warmer months, the timing of the wettest hour is also observed in the afternoon on the mainland and during the night on the Adriatic coast and islands. Preliminary analysis of trends in annual maximum sub-daily precipitation highlights a limitation arising from the insufficient availability of long and complete ombrographic measurement series. This limitation hinders trend calculation for all stations over the entire analyzed period. The majority of stations exhibit a trend of increased short-term heavy precipitation amounts from 1981 to 2020, with statistical significance observed only at a few stations. Comparing the means of intensity and duration indices in two climatological periods indicates an increase in the number of wet hours, sub-daily precipitation intensity, and average duration of wet spells, particularly in the latter 30-year period. This study represents the first climatological analysis of short-term precipitation in Croatia. The findings offer a valuable foundation for evaluating the risk of flash floods, as well as for climate modeling and adapting to climate change. Additionally, the results can form the basis for developing criteria for heavy rainfall warnings, which should be regularly monitored and revised due to climate changes.