The Lithuanian-born free agent averaged 7.5 points, 5.3 rebounds and 0.8 blocks in 53 games earlier this season with the Cavs before being traded to the Washington Wizards last month.
Ilgauskas did not appear in any games for the Wizards, who released the 7-foot-3 (2.2m) center after reaching an agreement on a contract buyout.
“The entire Cleveland Cavaliers organization … (is) thrilled that Zydrunas is coming back home to help us with our upcoming playoffs mission and hopefully, beyond,” Cavaliers owner Dan Gilbert said in a statement. “Things didn’t seem quite right around here without the big guy.”
Ilgauskas, 34, was drafted by the Cavaliers with the 20th overall pick of the 1996 NBA Draft, and has played his entire career in Cleveland.
He has career averages of 13.9 points, 7.7 rebounds and 1.7 blocks.
To make room for Ilgauskas, the team waived forward Darnell Jackson.
