Abstract: A pet cage capable of ready disassembly and erection for mounting within a window having a bottom rail and a stop, and projecting beyond the window opening. The pet cage consists of a 5-sided enclosure, including a hollow panel. An accordion-pleated panel assembly is removably connected to the enclosure for adjustably extending between the enclosure and the window stop. Upon disassembly, the panel assembly is removed from the enclosure and stored within the hollow panel so that the disassembled pet cage forms a single, compact, portable structure.