The liver and spleen size and the splanchnic vessel caliber were evaluated by means of real-time ultrasonography in 12 consecutive patients who underwent a partial hepatic resection for benign or malignant lesions. All parameters were evaluated before surgery and 14 days, 28 days, two months, and six months after the partial hepatic resection. The liver size, which was halved after the resection, progressively increased during the follow-up. The splanchnic veins showed, at 14 and 28 days, a significant increase in caliber and a reduced compliance to breathing, which progressively returned to normal levels. The spleen size increased after partial hepatectomy and remained enlarged throughout the study. Ultrasonography was able to detect that partial hepatic resection is followed by a progressive regeneration of the residual parenchyma and by a transient increase in portal pressure, which returns to normal levels when the liver regenerates.