Objective: This study aimed to explore the effects of age, sex, body mass index (BMI), and smoking on the diameter of the portal vein (PV). Materials and Methods: This quantitative descriptive study included 113 participants (61.9% males and 38.1% females) who underwent sonography. The participants were selected via convenience sampling. Patients with known cardiac, liver, or biliary diseases were excluded. The PV of each participant was evaluated and measured using a 3.5 MHz transducer and a standard liver sonography imaging protocol. Statistical analyses were performed using descriptive statistics, chi-square test, independent t-test, and Pearson correlations. Statistical significance was set at P < .05. Results: The mean age of the participants was 38 ± 16 years (range = 15–86 years). The mean PV diameter and BMI were 9.6 ± 2 mm (range = 4.9–16 mm) and 26.22 ± 8.5 (range = 15.2–39.7), respectively. The mean PV diameter of the participants who did and did not smoke was 10.5 ± 2.3 mm and 9.25 ± 1.8 mm, respectively. The PV diameter showed statistically significant associations with smoking status, age, and BMI ( P = .01, .007, and .022, respectively). Conclusion: The findings of this study suggest that the PV diameter may increase with smoking, age, and BMI; however, no correlation was observed between the PV diameter and sex.