Hedgehog had to be deflated after swelling to the size of a football
The female had inflated to twice its normal size and was found near Quedgeley, Gloucestershire.
She was so big she was seen by a passenger on a passing bus.
The hog was taken to Wild Hogs Hedgehog Rescue and diagnosed with balloon syndrome.
It only occurs in hedgehogs and is due to their ability to curl up meaning they have a gap under their skin.
Manager Emily Harper said: "The hedgehog was spotted by a man on the bus in a field.
''I deflated the hedgehog using a wide-gauge needle to release the trapped air.
''She was given pain relief and antibiotics and taken to our vet, Wood Veterinary Group.
''They carried out an x-ray to check for any internal injuries and completed the deflation.
''She will remain in our care on antibiotics and pain relief for at least a week.
''Balloon syndrome is unique to hedgehogs. They have a gap between the skin and the muscular-skeletal structure of their body.
''If a wound occurs, then infection can get into the gap.
''The outside skin heals over and the infection is trapped inside, releasing gases which cause the hedgehog to balloon.
''This is extremely painful and is fatal if not treated. The hedgehog was struggling to walk when she came in and her skin was stretched tightly.
''Sometimes balloon syndrome can be caused by punctured lung or emphysema but these were ruled out on the x-ray.''
People can donate towards its care and treatment at www.wildhogshedgehogrescue.org.uk or https://www.facebook.com/Hodgehegs
