Objectives: There are few studies of spontaneous hemorrhagic transformation (HT) after ischemic stroke (IS), and those that are available do not preclude the use of antithrombotic therapy after admission. We aimed to investigate the frequency and risk factors of spontaneous HT in patients who received no therapy between IS onset and the first instance of neurological imaging. Methods: We studied spontaneous HT using the China National Stroke Registry. Spontaneous HT was diagnosed on an initial computed tomography or magnetic resonance imaging scan within 14 days of IS onset. The risk factors associated with spontaneous HT were assessed using univariate analyses and multivariate logistic regression. Results: A total of 12,415 patients were diagnosed with IS, and among them, 114 (0.92%) had spontaneous HT. Multivariate analysis revealed that being female odds ratio (OR, 2.29; 95% CI, 1.52-3.44, p < 0.0001), excess alcohol consumption (OR, 2.17; 95% CI, 1.20-3.94, p = 0.0109), atrial fibrillation (OR, 2.15; 95% CI, 1.26-3.66, p = 0.0051), and a prolonged period between IS onset and initial imaging (1-7 days: OR, 1.64, 95% CI, 1.11-2.42, p = 0.0131; 7-14 days: OR, 3.12, 95% CI, 1.53-6.40, p = 0.0018) were positively associated with spontaneous HT. Discussion: Spontaneous HT occurred in 0.92% of the patients with IS in the acute stage. Being female, excess alcohol consumption, atrial fibrillation, and a prolonged period between IS onset and initial imaging were associated with an increased risk of spontaneous HT.