This retrospective study investigated the incidence, characteristics, and risk factors of bone fracture among a group of 518 adults with severe mental retardation between 25 and 75 years old. Data were collected from a large state developmental center in the Western United States between April 1, 1991 and March 31, 1996. Ninety-six of 271 males and 133 of 247 females experienced 291 fractures during the study period. Relative risk of fracture for all males was .658 compared to 1.540 for females. Menopausal status did not significantly influence the risk of fractures among females. Risk of fracture by self-feeding ability ranged from 1.675 for individuals who were tube fed to .343 for those requiring no assistance during meals. As a group, individuals with a body mass index (BMI) less than 20 were at the greatest risk of fracture (RR=2.416). Males with BMI values between 20-25 (RR=.560) and greater than 25 (RR=.373) had a decreased risk of fracture. Ambulatory males and females had a significantly decreased risk of fracture (RR=.356 and .559 respectively). Rib, femur, vertebrae, and radial fractures accounted for nearly 60% of all fractures. The etiology of the 41% of fractures was of unknown origin. Transfers by developmental training personnel (10.3%), falls to the ground (15.8%), and accidents (32.6%) were also frequently related to fracture cause. Logistic regression analysis revealed the occurrence of any fracture was significantly associated with ambulation, calcium intake, body weight, self-feeding ability, and body mass index. / Graduation date: 1997