Background: Hypertension is one of the dangerous chronic diseases. In the treatment of hypertension, controlling blood pressure to achieve treatment target is paramount to prevent dangerous complications and death. The study was conducted to identify the percentage of hypertensive patients who do not achieve treatment target among outpatients at the internal medicine clinic, Hue University of Medicine and Pharmacy Hospital, and explore some related factors. Methods: A cross-sectional study was conducted among 403 hypertensive patients treated as outpatients at the internal medicine clinic. A multivariate logistic regression model was used to identify the related factors. Results: 46.4% of hypertensive patients did not reach the treatment target. Factors related to uncontrolled hypertension were male, non-religion, comorbidities, no reduction in salt intake, the use of coffee/tea, and non-compliance with medication (p < 0.05). Conclusions: The rate of patients with uncontrolled hypertension was still high. The health sector should consider establishing an outpatient management team; strengthening communication activities and advice on diet and drug use in parallel with medical examination and treatment.