January – February – March – April – May – June – July – August – September – October – November – December
- May 1, 1900 - Charles Herbert Allen becomes the first civil governor of Puerto Rico (appointed) since the end of the Spanish–American War.
- May 5, 2007 - Death of José Aponte de la Torre, long-time mayor of Carolina (b. 1941)
- May 6, 1975 - Birth of Germán Figueroa, professional wrestler
- May 8, 1926 - Birth of Felipe Rodriguez, singer of boleros (d. 1999)
- May 9, 2004 - Twenty-two passengers, two stoweaways and crew are injured when an American Eagle ATR 42, flight 1450, crash-lands in San Juan, Puerto Rico.
- May 10, 1885 - Birth of Antonio Fernós-Isern, the first Puerto Rican cardiologist and its longest serving resident commissioner (d. 1974)
- May 10, 1898 - In one of the first conflicts of the Spanish–American War, Spanish forces at Fort San Cristóbal exchange fire with the USS Yale.
- May 12, 1898 - 12 American ships bombard parts of San Juan.
- May 12, 1980 - Birth of Felipe López, Mayor League Baseball shortstop
- May 12, 1981 - Birth of Manuel Narvaez, professional basketball player
- May 13, 1829 - Birth of Segundo Ruiz Belvis, dedicated abolitionist who also fought for Puerto Rico's right to independence (d. 1867)
- May 14, 1876 - Birth of Luis Lloréns Torres, poet, journalist, playwright, and politician (d. 1944)
- May 17, 1917 - Death of Francisco Oller, artist (b. 1833)
- May 21, 1962 - El Gran Combo debuts on Puerto Rican radio.
- May 22, 1772 - The Municipality of Bayamón is founded.
- May 22, 1772 - The Municipality of Orocovis is founded.
- May 22, 1772 - The Municipality of Quebradillas is founded.
- May 23, 1919 - Birth of Ruth Fernández, singer
- May 23, 1985 - Birth of Peter John Ramos, professional basketball player
- May 24, 1962 - Birth of Héctor Camacho, former professional boxing champion
- May 25, 1838 - The Municipality of Aguas Buenas is founded.
- May 25, 1975 - Birth of Gilbert Cosme, professional wrestler
- May 26, 1999 - Death of Felipe Rodriguez, singer of boleros (b. 1926)
- May 29, 1984 - Birth of Carmelo Anthony, professional basketball player
- May 30, 1981 - Death of Ana María O'Neill, advocate of women's rights (b. 1894)
- May 30, 2001 - Death of Jaime Benítez, author, academic, politician (b. 1908)