Three cases of jellyfish envenomation which occurred in the Indian Ocean and the Andaman Sea are reported. In each instance the stinging occurred on the upper extremities, and impaired the circulation to the stung limb(s), with absent distal arterial pulses, regional cyanosis, and the threat of distal gangrene. One of the patients is seriously and permanently handicapped, with bilateral upper-limb numbness and paresis; another patient has permanent sensory loss; the third patient, who also had brachial-artery narrowing that was demonstrated by angiography, made an uneventful recovery. The first two patients underwent surgical fasciotomy, whereas surgical exploration was performed on the third patient. Reduced blood flow in the major arteries of the limbs was observed directly in each case. Further, the arterial segment that primarily was affected, in each case, appeared to be that which underlay the actual site of the sting. All patients were young persons with no previous history of vascular disease. These cases corroborate the vascular and neurogenic injury, which previously have been reported in experimental animals and in human patients, that may result from jellyfish venoms.