The present study was performed to investigate the relationship between the concentrations of tissue-type plasminogen activator (t-PA) and plasminogen activator inhibitor (PAI) and the CT images in 23 cases of chronic subdural hematomas (SDHs). The concentrations of t-PA and PAI-1 were quantified by enzyme-linked immunosorbent assay (ELISA). Chronic SDHs were divided into five groups according to their appearance on computed tomography: high-density (n = 4), isodensity (n = 8), low-density (n = 5), mixed-density (n = 3), layering (n = 3) types. The volume of hematoma was measured with an image analyzing software program. The concentrations of t-PA were higher in layering (41.2 ± 0.3 ng/ml, mean ± standard error of the mean) and high-density (40.0 ± 1.1 ng/ml) types compared to those of low-density (23.3 ± 4.1 ng/ml) and iso-density (25.1 ± 3.7 ng/ml) types. The concentrations of PAI-1 were lower in layering (95.9 ± 1.0 ng/ml) and high-density (103.4 ± 34.5 ng/ml) types compared to that of low-density (192.5 ± 2.6 ng/ml) type. So the ratio between t-PA and PAI-1 (t-PA/PAI) was greater in layering and high-density types. The volume of hematoma was larger in mixed-density and layering types but statistically insignificant. These results presumably suggest that the ratio between t-PA and PAI concentration may contribute to the pathogenesis of the chronic SDH.