Abstract: A party balloon (10) comprises an expansible membrane with an inlet port (15) to allow entry of gas upon inflation and an illumination device comprising a light emitting diode (LED) (50) powered by at least one battery (54) is mounted inside the balloon (10). In this respect, the illumination device (50) has a projection (58) whereby it is attached to the expansible membrane, inside the balloon, by a clip or O-ring (59) fitted onto the projection (58) from outside the balloon. A strip of insulating material (53) is initially located between the battery or batteries (54) and the LED (50) and is capable of being withdrawn, e g prior to or upon inflation of the balloon (10), to light up the LED and the balloon.