The participants are the patients referred from the 15 primary care centers (400.000 inhabitants) to the Hospital de la Santa Creu i Sant Pau emergency department with suspected DVT. We will enter physical examination and anamnesis variables, Wells and Oudega's rules variables, D-Dimer value and ultrasonography result. The outcome variables are the cost (€) of each possible way of diagnostic approach and the effectiveness will be measured by the ultrasonography result, which confirms or excludes the diagnosis. The sample will include 437 patients. A decision tree will be developed to analyze the different diagnostic options in DVT cases, using standard notation.