Cristina Yang first said that Burke's apartment was so clean you could do a surgery here.
Burke first asked Cristina to move into his apartment with him in Much too Much. After a while she accepted, but was secretly keeping her old one. After Burke found out, Cristina gave it up and moved in properly.
They continued to live there together until Burke left her on the wedding day and didn't return.
Despite it being Burke's old apartment, Cristina continued to live there alone. Jane Burke collected the rest of Burke's things some weeks after Burke left her. Cristina almost allowed Richard Webber to move in with her but refused when he hired Erica Hahn at Seattle Grace Hospital. Later, Callie moved in.
When Izzie feared that she was going to be kicked out of Meredith's House, she showed Cristina a flier for another apartment hinting that she and Cristina should live there. Cristina misinterpreted and she and Callie moved there instead.