Retrospective evaluation of local low-dose thrombolysis for treatment of venous port-catheter thrombosis. A total of 1,031 patients with dysfunctional port systems underwent port angiography depicting 181 patients with thrombosis around the port-catheter. A total of 165 patients (male 35, female 130; age 57.3±12.9 [20-83]years) underwent thrombolysis by single injection of 3mg alteplase into the port system. Patients were followed up by clinical and angiographic/radiological port controls the next day and 12.9±17.9 [1-81]months on the basis of regular oncologic staging examinations. Thrombosis occurred 10.1±19.3 [median 2.9] months after port implantation and was clinically suspected by difficult blood aspiration in 146 of 181 (80.7%) and high resistance to injection fluids in 75 (41.4%) patients. A predictor for angiographically confirmed port-catheter thrombosis was a combination of both (73, 40.3% patients) (Fisher's exact test p<0.0001; positive predictive value 0.8977), or suboptimal (not cavoatrial) port-catheter position (92, 50.8% patients) (p=0.0047; positive predictive value 0.8276). The cumulative success rate of thrombolysis was 92.7% (153 of 165 patients). Initial thrombolysis was effective in 127 (77.0%) patients. Repeated (up to 6 times) thrombolysis was effective in 26 of 31 patients after second or third thrombolysis. Extensive central venous thrombosis (9 patients) predicted ineffective thrombolysis (p<0.0001). Primary patency of successfully treated devices was 92.8% at 1month and 84.9% at 3months. Rethrombosis occurred in 27 patients after 4.4±6.6 (median 1.8) months. Primary rethrombolysis was effective in 22 (81.5%) patients. Cumulative patency was 100% at 3months. Difficult aspiration combined with high resistance to injection fluids or suboptimal port-catheter position are strong independent predictors for port-catheter thrombosis. Local low-dose thrombolysis or repeat thrombolysis is safe and effective in the absence of large central venous thrombosis.