External pressure is the most frequently considered stress factor in the formation of ulcers. A review and analysis of existing literature addressing the relationship between pressure ulcer prevalence and interface pressures at various anatomic sites was conducted. Results suggest a nearly non-existent or slightly negative correlation between interface pressure and ulcer prevalence in general and spinal cord injured populations, respectively. Despite limitations of the analysis methods used, the observed lack of a direct relationship confirms the results of other studies and suggests that ulcer formation also may involve factors secondary to pressure and mechanical factors (eg, temperature, moisture, duration of the applied load, atrophy, and posture). Based on currently available information, clinicians should include these considerations when selecting a support surface. Studies directly relating primary stress factors and tissue viability with prevalence and incidence of pressure ulcers are needed to better understand the benefits of pressure-relieving support surfaces and to improve the effectiveness of prevention and treatment.