Objective To determine the incidence of deep vein thrombosis (DVT) in patients diagnosed with superficial thrombophlebitis (STP) after presenting to an outpatient DVT service.

Method Six month prospective follow-up by telephone of patients diagnosed with STP after presenting to an outpatient DVT service. All patients who returned during follow-up with clinically suspected venous thrombosis underwent diagnostic testing (compression ultrasound).

Results A total of 79 patients was diagnosed with STP after the exclusion of DVT with the diagnostic protocol. The incidence of a subsequent diagnosis of DVT on 6-month follow-up was three out of 79 patients (4%, 95% CI 0.8% to 11%).

Conclusion Although STP is generally considered benign, there is a risk that it may coexist or develop into DVT. The underlying cause of STP should be considered and patients with significant risk factors should be advised to monitor their symptoms closely with regard to potential DVT formation.