The objective of this research was to investigate the frequency of heavy rainfall over the island of Puerto Rico and its different climatic regions. We defined heavy precipitation as 4 inches of rainfall or more in a 24 hour period. We chose the days of precipitation with heavy precipitation and classified it by heavy rainfall (4 in. ≤ P < 6in.) and very heavy rainfall (P ≥ 6in.). The total number of days was 161 days, 90 days was during hurricanes season (56%) and 71 during transition season (44%). The years of greater activity of intense rainfall were 1983, 1992 and 1998. With heavy precipitation event only Southern Slope and Western Interior presented increase. In very heavy precipitation event only Western Interior and Eastern Interior presented increase, while North Coastal and North Slope presented decrease. This research is part of the first phase of another proposal whose goal is to identify and describe the synoptic conditions that can cause heavy precipitation in Puerto Rico and U.S. Virgin Islands.