a portable security grill apparatus which may be installed in window openings of buildings includes two rectangular grill sections longitudinally telescopically fastened to one another . opposite longitudinal ends of the two grill sections have beams disposed perpendicularly to the axis of longitudinal telescoping movability of the two grill sections , the beams having flat outer surfaces adapted to abut a window edge at one end of the grill apparatus , and a window frame edge , at the other end of the apparatus . at least one toggle clamp connected between telescopically joined members of the two grill sections is capable of exerting a large outward extension force when in a closed , clamped position , thereby exerting compressive forces on the window and window frame sufficient to prevent the grill apparatus from being removed from the window opening .