Reduced plasminogen activity with a normal level of antigen is commonly observed in Japanese individuals. The first reported patient with plasminogen deficiency was accompanied with deep vein thrombosis. The present study examines whether heterozygous or homozygous deficiency of plasminogen is a risk factor for thrombotic disease. This study measures the plasminogen activity of 4517 individuals in the general population, determines the cut-off to define plasminogen deficiency, and identifies plasminogen deficiencies in the control groups and thrombotic disease groups. In another study, we examined the phenotypes of consecutive patients with homozygous plasminogen deficiency detected in our hospital. We found 173 and two of 4517 individuals to have heterozygous and homozygous deficiency with normal plasminogen antigen level, respectively, and 19 to have heterozygous deficiency with reduced antigen levels. The incidence of plasminogen deficiency in an age- and sex-matched control group (13/324, 4.01% for deep vein thrombosis or 13/330, 3.94% for stroke) selected from the 4517 individuals was not significantly different from those in patients with deep vein thrombosis (3/108, 2.78%) or cardioembolic stroke (6/110, 5.55%). Among 19 patients with homozygous plasminogen deficiency showing about 10% plasminogen activity, none had deep vein thrombosis. These findings indicate that neither heterozygous nor homozygous plasminogen deficiency constitutes a significant risk factor for thrombotic disease.