Alex O'Loughlin and Scott Caan were born just a day apart. Alex in Canberra, Australian Capital Territory (A.C.T), Australia, and Scott in Los Angeles, California. Since Australia is one day ahead of the United States, they were essentially born on the same day.
This show premiered on September 20, 2010, forty-two years to the day from the premiere of Hawaii Five-O (1968).
During the opening credits, the camera zooms in on McGarrett (Alex O'Loughlin) standing on a balcony. It is the same balcony, on the same building, on which McGarrett (Jack Lord) was standing during the opening credits of Hawaii Five-O (1968).
When the show premiered in 2010, the character of Kono Kalakaua (Grace Park) was written to be a rookie cop in her mid-twenties. Park was 36 years old when the show premiered. Her character is supposed to be younger than Steve McGarrett (Alex O'Loughlin). In real life, Park is two years older than O'Loughlin.
On this show, season two, episode nineteen, "Kalele", Edward Asner played a jeweler called August March. He played the same character on Hawaii Five-O (1968), season eight, episode fifteen, "Wooden Model of a Rat". The new episode used footage of his original appearance, explaining in the new continuity that he was arrested in his youth by a cop named McGarrett (Steve's father). Asner played March again on this show, season three, episode two, "Kanalua".