The team announced the deal Thursday. Agent Mark Guy confirmed the terms in an email to The Associated Press.
Cizikas will count $3.35 million against the salary cap through the 2020-21 NHL season. He was at $1 million on his previous contract.
"Casey has developed into a highly dependable two-way center, and we're pleased to sign him through 2021," general manager Garth Snow said. "His energy and passion both on the ice and in the community make him an invaluable piece of our lineup."
The 25-year-old Cizikas set a career high in points last season with 30 on eight goals and 22 assists for the Islanders, who reached the second round of the playoffs for the first time since 1993. He had three assists in 11 playoff games.
Cizikas has 29 goals and 54 assists for 83 career points since making his NHL debut in 2012. The Toronto native was a fourth-round pick in 2009.
Set to be a restricted free agent July 1, Cizikas now trails only defensemen Nick Leddy and Johnny Boychuk in future years under contract. Leddy and Boychuk are signed through 2022.
"I'm thrilled to remain a New York Islander for the next five years," Cizikas said. "The organization has been first class ever since I was drafted and we've come so far as a team during my time here. I'm excited to continue to be a part of this group as we build towards the ultimate goal, the Stanley Cup."
(TM and © Copyright 2016 CBS Radio Inc. and its relevant subsidiaries. CBS RADIO and EYE Logo TM and Copyright 2016 CBS Broadcasting Inc. Used under license. All Rights Reserved. This material may not be published, broadcast, rewritten, or redistributed. The Associated Press contributed to this report.)
for more features.