Objective: To determine the correlation between portal vein diameter and spleen size (craniocaudal). Methodology: The study was conducted at the University Ultrasound Clinic, The University of Lahore, Lahore Pakistan from 1st January to 1st July 2013. All the individuals who referred for abdominal sonographic examination, including male, female, older and younger were conveniently included in the study, voluntarily, irrespective of the disease state. Ultrasonographic measurements of the caudocranial length of the spleen and portal vein were carried out on all of the one thousand subjects. The subject position for spleen was supine or right posterior oblique during suspended inspiration and right anterior oblique position for portal vein diameter with quiet respiration. The correlation between the splenic length and portal vein diameter was evaluated. Result: A total of 1000 subjects; 36.9% females and 63.1% males aged from 4 to 79 years. The mean splenic length was 10.29 ± 1.89 cm. The mean portal vein diameter was 10.27 ± 1.78 mm. A statistically significant correlation was found between the spleen size and portal vein diameter; the Pearson correlation was significant at the 0.01 level. Conclusion: Portal vein diameter is directly correlated to splenic caudocranial length. A regression formula was developed to measure the splenic length from the calculation of portal vein diameter.