Decompression illness (DCI) describes a syndrome complex caused by inert gas bubbles generated by an inappropriate rate of reduction in ambient environmental pressure or decompression. This “umbrella term” covers both traditional decompression sickness caused by in-situ bubble formation from dissolved inert gas and arterial gas embolism (AGE), in which alveolar gas or venous gas emboli (via shunts or by-passing pulmonary vessels) are introduced into arterial circulation. DCI occurs in divers, compressed air workers, aviators, and astronauts, but AGE could also arise from iatrogenic causes unrelated to decompression. A hundred years ago, serious manifestations and deaths were frequent in divers and caisson workers due to DCI, but they decreased greatly when decompression stops were introduced in diving practice. This review article is of interest to the doctors who face the dilemma of treating the rare syndrome of DCI that could present in the clinical spectrum ranging from itching and minor pain to severe neurological symptoms or other systemic pathology. The first aid lies in the administration of 100% oxygen, and definitive treatment is therapeutic recompression. With appropriate and adequate treatment, recovery is complete, but some severe cases may have lifelong residual deficits, even after extended and multiple recompressions.