-Objective: Heterotopic ossification (HO) is a complication of the spinal cord injury (SCI). It can result in anchylosis, harming the rehabilitation and quality of life. Previous publications had not elucidated the relation between possible independent variables, the aim of this study. Method: From 230 patients with SCI, admitted in 1998 at Hospital SARAH Brasilia, 33 with HO (14.3%; CI95% 10.1-19.6) were compared with 33 controls. The risk factors had been tested in bivariate analysis and in a model of logistic regression. Results: Spasticity (odds ratio=3.8; CI95% 1.15-12.30), number of pressure ulcers (2.1; CI95% 1.08-3.89) and time lapsed since the injury (1.1; CI95% 1.02-1.24) were independently associated with HO. There was a confounder effect among these variables, without interaction. Conclusion: Spasticity, pressure ulcer and time of injury are associated with HO in spinal cord injury. The first two factors can be prevented and treatable.Key wORdS: heterotopic ossification, spinal cord injuries, pressure ulcer, muscle spasticity, risk factors, multivariate analysis. fatores de risco da ossificação heterotópica na lesão medular traumáticaResumo -Objetivo: A ossificação heterotópica (OH) é uma complicação da lesão medular traumática (LMT). Pode resultar em anquilose, prejudicando a reabilitação e a qualidade de vida. estudos prévios não elucidaram a relação entre as potenciais variáveis independentes, propósito desse estudo. Método: de 230 pacientes com LMT, admitidos em 1998 no Hospital SARAH Brasília, 33 tiveram o diagnóstico de OH (14,4%; IC95% 10,1-19,6), que foram comparados a 33 controles. Os fatores de risco foram testados de forma bivariada e num modelo de regressão logística. Resultados: espasticidade (razão de chances 3,8; IC95% 1,15-12,30), número de escaras (2,1; 1,08-3,89) e tempo de lesão (1,1; 1,02-1,24) encontraram-se associadas, de forma independente, à presença de OH. Havia um efeito confundidor entre essas variáveis, porém sem interação. Conclusão: espasticidade, escaras e tempo de lesão estão associados à OH na lesão medular traumática. Os dois primeiros são passíveis de prevenção e tratamento. PALAvRAS-CHAve: ossificação heterotópica, traumatismos da medula espinal, úlcera de pressão, espasticidade muscular, fatores de risco, análise multivariada. Heterotopic ossification is a common complication of traumatic spinal cord injuries with a prevalence ranging from 5 to 50%, depending upon the studies design and the diagnosis method [1][2][3][4] . The progression of heterotopic ossification may lead to decreases in the range of motion and anchylosis and has a negative impact on the rehabilitation processes 3 . The most affected joints are the hips (60%-70%) and knees (20%-30%) 1 . The etiology and pathogenesis of heterotopic ossification are still unknown, but some factors appear to favor its onset in patients with traumatic spinal cord injuries: gender, age, completeness of the injury, presence of spasticity and decubitus ulcers [5][6][7][8] . However, various confounding and int...