Thrombocytopenia, microangiopathic hemolytic anemia, and elevated serum lactate dehydrogenase (LDH) clinically characterize thrombotic microangiopathy (TMA), which is frequently recognized among patients with malignant hypertension (MH). Sixteen consecutive patients with MH were retrospectively investigated over a 7-year period and clinical features of the subjects with TMA were evaluated. We confirmed TMA relevant to MH by the normalization of the platelet count and LDH after adequate blood pressure (BP) control was achieved. Thrombotic microangiopathy was found in 7 (44%) of 16 patients. All 7 patients had an elevated plasma renin activity (PRA). Although no significant differences were observed in PRA, the patients with TMA had a significantly higher plasma aldosterone (ALDO) (median: 403 pg/ml; IR: 305 to 568) in comparison to those without TMA (median: 220 pg/ml; IR: 147 to 287; p = 0.013). Overall, ALDO correlated with LDH (r = 0.634, p = 0.0095). However, no significant association was observed between PRA and LDH (r = 0.336, p = 0.2263). The median platelet count nadir of the patients with TMA was 8.4 × 10(4) per μl (IR: 7.15 to 9.95). Thrombocytopenia and elevated LDH were normalized, along with a gradual improvement of BP within an average of 5 days and 21.7 days, respectively. These results suggest that ALDO, but not PRA, may act as a potent indicator of the magnitude of vascular and organ damage related to TMA among patients with malignant hypertension (MH).