Introduction: pressure ulcers are a public health issue and affect individuals at the bio-psycho-social levels.  Risk scales have been developed to help pressure ulcer prevention. Aim: the aim of the study was to compare the performance of Braden's and Waterlow's Scales as predictors for the development of pressure ulcers (PU) in hospitalized patients. Methods: this study was a prospective cohort methodological type developed in two private hospitals in São Paulo, Brazil.  After approval from Ethics Committees, 170 hospitalized patients were assessed from January through July 2006 during at least one week. The patients were evaluated for PU risk factors using Braden and Waterlow scales and had their skin examined every 48 hours.  During the hospitalization period, each patient was examined at least tree times to be considered for analysis. The data were analyzed through multivariate regression including risk factors derived from both scales and demographic (sex and age) and clinical variables (hospitalization days, type and local of treatment) at three first assessments. Results: 57% of the patients were male, with an average age of 67 years old. With major Wald estimative, shear/friction and sensory perception of Braden scale and mobility of Waterlow were the most important predictors at the first assessment (p<0.001); sensory perception and activity of Braden scale and skin type and mobility of Waterlow were the most important at second (p<0.001); and sensory perception of Braden and appetite, mobility and skin type of Waterlow scale, at the third (p<0.001). Other demographic and clinical variables as sex, hospitalization time and type of treatment were important PU development predictors (p<0.001). Conclusion: The study shows that Braden sensory perception sub scale and Waterlow mobility subscale were the common relevant risk factors present on the first three assessments of hospitalized patients.