The Sequential Compression Device (SCD) is frequently the sole measure used to prevent deep venous thrombosis (DVT) in trauma patients. The purpose of this study was to evaluate the compliance with physician orders for the application of SCD prophylaxis among nonambulatory trauma patients at risk for DVT. We conducted a prospective observational study at two Level I university-affiliated trauma centers. Nonambulatory trauma patients were observed during their early postadmission period in a non-critical care setting. Six observations were made as to proper SCD applications during a 24-hour period (two times in the morning shift, two in the evening shift, and two overnight). "Full compliance" was defined as SCD on and functioning properly in all six observations. In a total of 1343 observations in 227 patients only 42 patients (19%) were fully compliant. The devices were on and functioning in 712 (53%) observations. Among the 185 patients who were not fully compliant DVT risk factors were common (83%) and adjunctive heparin prophylaxis was infrequent (27%). The most common times for "noncompliant" observations were early afternoon and midmorning. On multivariate analysis only spinal column injury correlated with increased compliance. In nearly half of the observations trauma patients at risk for DVT were not receiving their SCD prophylaxis as per physician orders. Fewer than 20 per cent of patients had the devices on and functioning during each of the six observations during a 24-hour period. These data point to the need for education of hospital staff and for additional prophylactic measures in at-risk patients.