U.S. Army hypobaric chamber operations over a 63-month period were retrospectively reviewed, and incidence rates for decompression sickness were calculated. The overall incidence rate was 1.38/1000 exposures. The rate for interior technicians monitoring chamber operations was 6.16/1000 exposures. The rate for students was 0.64/1000 exposures. The increased incidence of decompression sickness for technicians was especially pronounced for the 10,668-m and 13,106-m flight profiles. Rapid decompression after the 7,620-m flight profile did not appear to increase the incidence of decompression sickness.