Background: The aim of this study was to investigate whether progression or fluctuation of transient ischemic attack (TIA) symptoms is a predictor of subsequent stroke. Methods: We prospectively analyzed 113 consecutive patients admitted with a diagnosis of classical TIA with symptom duration of less than 24 h. We assessed the background characteristics, TIA symptoms, attack characteristics, results of in-hospital examinations, and prescription of antithrombotic agents on discharge for each patient. We then analyzed the factors related to progression or fluctuation of TIA symptoms. Results: Of the 113 patients, 35 (31.0%) exhibited symptom progression or fluctuation. Subsequent stroke occurred in 12 (10.6%) patients within 180 days. Symptom progression or fluctuation was significantly related to the TIA symptoms of speech disturbance, hemiparesis, and monoparesis, and were also related to subsequent stroke occurrence within 90 days (29 vs. 3%, p = 0.004) and 180 days (23 vs. 5%, p = 0.008). In a logistic regression model analysis, symptom progression or fluctuation was a significant predictor of subsequent stroke within 90 days (odds ratio = 7.65, 95% CI 1.27–46.06) and 180 days (odds ratio = 4.44, 95% CI 1.08–18.13), independently of other predictors demonstrated in previous studies. Conclusions: Progression or fluctuation of TIA symptoms may be an important predictor of subsequent stroke. A detailed interview about the characteristics of each attack is also indispensable for the provision of appropriate care to TIA patients.