Type II altitude-related decompression sickness (DCS), due to its wide spectrum of symptoms, is often difficult to diagnose. This difficulty sometimes leads unnecessarily to the permanent grounding of an experienced aviator. So that this condition could be better understood, a total of 133 cases of Type II altitude DCS (on file at the United States Air Force Hyperbaric Medicine Division, School of Aerospace Medicine, Brooks AFB, TX) were reviewed. Most cases (94.7%) followed altitude chamber training. The most common manifestation was joint pain (43.6%), associated with headache (42.1%), visual disturbances (30.1%), and limb paresthesia (27.8%). The next most common symptoms were, in order of decreasing frequency: mental confusion (24.8%), limb numbness (16.5%), and extreme fatigue (10.5%). Spinal cord involvement, chokes, and unconsciousness were rare (6.9%, 6%, and 1.5%, respectively). Hyperbaric oxygen treatment produced fully successful results in 97.7% of the cases. Only 2.3% of the cases resulted in residual deficit; no deaths occurred. A thorough knowledge of the differential diagnosis and predisposing factors is essential to narrow the margins of error in the diagnosis and prevention of decompression sickness in the operational or training environment. A recommendation for favorable consideration of waiver action for those aviators who suffered Type II DCS is presented. These recommendations are based on a unique classification of the severity of symptoms.