Purpose To analyze the sources of errors and discuss the techniques to eliminate pitfalls in detecting deep vein thrombosis (DVT) of the proximal lower extremities with color duplex ultrasonography (CDUS). Methods Sixty-eight cases with initial and repeat venous CDUS of the proximal lower extremities were retrospectively reviewed. The repeat was done within 24 hours after initial CDUS scanning. Comparing repeated images to initial ones, the pitfalls and sources of error in CDUS of the proximal lower extremities were discussed. Results In total 68 repeat studies, there were 62 results as same as initials and 4 cases of false negative DVT and 2 cases of false positive DVT. Conclusion Venous CDUS in detecting DVT is observer dependent. Some pitfalls and errors can be eliminated and corrected with proper scan techniques. CDUS is the most valuable imaging modality for assessing suspected DVT in the proximal lower extremities.