To the Editor: We anecdotally observed that the frequency of deep vein thrombosis (DVT) seemed low in elderly patients in chronic care facilities despite the infrequent use of antithrombotic prophylaxis and the almost universal coexistence in these patients of two risk factors for DVT: old age and chronic rest.1–3 We performed a prospective observational study to estimate the prevalence of DVT in chronically bedridden elderly individuals admitted to chronic care facilities and the incidence of DVT in such individuals during the first 120 days after admission. Subjects from four different chronic care facilities participated in the study. These facilities can provide chronic care to a maximum of 593 extremely poor or abandoned older people, whom the local government social agencies classify as indigent. Eligible subjects were all bedridden individuals aged 60 and older admitted to any of the participating chronic care facilities. Those with cancer, thrombophilia, autoimmune disorders, and prophylactic or therapeutic anticoagulation were excluded. DVT was diagnosed using Doppler ultrasound of the lower extremities combined with physical examination. Each subject underwent physical examination and venous Doppler ultrasound with a 6.5 MHz high-frequency transducer on admission and at 30, 60, and 120 days. Additional venous Doppler ultrasounds were planned if an individual developed lower extremity edema, pain, erythema, or heat during the follow-up period. If an ultrasound performed on a symptomatic patient was reported as negative, a 7-day follow-up ultrasound was planned before classifying the individual as negative for DVT. Prevalence was calculated as the number of DVT cases diagnosed on admission divided by the total number of patients admitted during the study period. Incidence was calculated as the number of DVT cases diagnosed during the 120 days of follow-up divided by the total number of individuals without a diagnosis of DVT on admission. Sample size was calculated using the following assumptions: estimated incidence of 6%, a confidence interval (CI) of 95%, and a margin of error of 5%. Accordingly, a convenience sample of 87 individuals was targeted. The ethics and research committees of the Fundación Universitaria de Ciencias de la Salud, Hospital de San José, approved the study. Eighty-seven subjects were prospectively evaluated between June 2004 and July 2005; 52 (59.8%) were women, and 35 (40.2%) were men. The mean age±standard deviation was 78.5±11.5 (range 60–104). All individuals had at least one comorbid condition. The most frequent comorbidities were high blood pressure (50.6%), cerebrovascular disease (26.4%), varicose vein disease (21.8%), chronic obstructive pulmonary disease (20.7%), heart failure (12.6%), and obesity (12.6%). DVT was diagnosed on admission in three of the 87 subjects, corresponding to a prevalence of 3% (95% CI=0–7.2%). All patients without DVT on admission completed 120 days of follow-up, and none had DVT, giving an estimated DVT incidence of 0%. The estimated prevalence and incidence of lower extremity DVT in chronically bedridden elderly individuals is low. Our study minimized selection and misclassification bias, favoring validity of the estimates. Based on our results, the risk of antithrombotic prophylaxis in this population seems to outweigh its possible benefit. We do not recommend the use of antithrombotic prophylaxis in chronically bedridden elderly individuals. The authors are indebted to the patients and staff of the four chronic care homes that participated in the study: San Pedro Claver, Bogotá; Hermanitas de los Pobres Micasa Calle 63, Bogotá; Micasa Hermanitas de los Pobres Carrera 10, Bogotá; Fundación Hogar San Francisco de Asis Nazareth, Zipaquirá. The authors had full access to all of the data in the study and take responsibility for the integrity of the data and the accuracy of the data analysis. Financial Disclosures: None. Author Contributions: Adelheide Valderrama, Javier Del Castillo, Juan C. Ortega, and Gustavo Guío: study design, subject recruitment, data collection, manuscript preparation. Carlos A. DiazGranados: study design, data collection, data analysis, manuscript preparation. José I. Hernández: study design, subject recruitment, manuscript preparation. Eduardo Molano: study design, data collection, manuscript preparation. Sponsor's Role: This study was conducted with institutional financial support from the Fundación Universitaria de Ciencias de la Salud, Bogotá, Colombia. The sponsor had no direct role in the design, methods, subject recruitment, data collections, analysis, or preparation of this letter.