The optimal treatment of isolated distal deep vein thrombosis (ID-DVT) is still controversial. A complete anticoagulation as soon as the diagnosis is made is recommended by some authors. Alternatively, other authors suggest to perform serial ultrasonography assessments to detect the possible extension of DVT towards proximal veins. Only in this case the treatment should be initiated. Furthermore, the optimal duration of treatment is far from established. The Treatment of Isolated Calf Thrombosis (TICT) study was set up to assess the efficacy and safety of a particular treatment regimen of ID-DVT based on low molecular weight heparins (LMWH). The drug treatment consisted of a twice-daily subcutaneous administration of a full dose of weight-adjusted LMWH for one week, followed by a half dose of LMWH administered once-daily for another three weeks. At the end of the four-week period of treatment, a colour-coded Doppler ultrasonography (CCDU) assessment was scheduled and after three months a follow-up visit was performed. If a patient was unable to attend the visit, he was contacted by a phone-call to assess if any adverse events occurred. The study enrolled 192 outpatients with ID-DVT confirmed by CCDU. Twenty-one out of 192 patients (10.9%) were excluded for violation of protocol. Thus 171 (39.9% men, mean age of 60.45 years ) were eligible and were included in the study. Sixty-one patients (36.6%) presented an unprovoked ID-DVT. Events during the period of treatment (4 weeks). Ten out of 171 patients (5.8%) had complications: five patients showed an extension proximal to the knee (2.9%) all with an unprovoked ID-DVT; two showed an extension of thrombus within the distal veins. Three patients (1.7%) suffered from minor bleeding; there was no major bleeding. Further events during three months of observation occurred. Five patients had thrombus recurrences: four patients showed a proximal DVT (3 with a previous unprovoked ID-DVT, 1 with a previous ID-DVT secondary to a traumatic leg fracture, with persistent difficulty of deambulation); one, with a previous secondary thrombosis, showed a ID-DVT. In our study only 2.9% of patients with ID-DVT showed a progression of thrombosis to proximal deep veins; the majority of thrombus progression, during the treatment period, was observed in patients with unprovoked ID-DVT. Our results support the usefulness of a prolonged treatment in unprovoked ID-DVT.