Idiopathic noncirrhotic portal hypertension (NCPH) is an infrequent but possibly underestimated cryptogenetic liver disease recently described in small series of HIV-infected patients. The exposure to antiretroviral drugs, a direct role of HIV itself, microbial translocation from the gut, or a thrombophilic propensity have been suggested as possible pathogenic mechanisms. In this case control study, we describe 11 HIV-infected patients with idiopathic NCPH and compare the activity of protein C and S, and soluble CD14 levels (a surrogate marker of the translocation of intestinal bacterial products) with 10 age- and gender-matched HIV-infected controls with no liver disease. The clinical presentation of the 11 patients with NCPH was characterised by acute variceal bleeding (2/11), ascites (2/11), portal thrombosis (2/11), and ultrasonographic and endoscopic signs of portal hypertension (11/11), with slightly high alanine transaminase (ALT) and γglutamyl transpeptidase (γ-GT) levels. The FibroScan median liver stiffness was 8.1 kPa, which is inconsistent with significant fibrosis, and nodular regenerative hyperplasia was diagnosed in the 5 patients who underwent liver biopsy. The NCPH patients showed no impairment of hepatic synthesis, but had lower serum albumin levels and a higher international normalized ratio (INR) than the controls (p = 0.01), and lower protein C and S activity, although within the normal range (p = 0.02 and 0.3, respectively). No significant difference in soluble CD14 was seen between the two groups. In conclusion, the etiology of NCHP is not still established, but in order to prevent the dramatic complications of portal hypertension, all HIV-infected patients with unexplained liver enzyme abnormalities or thrombocytopenia should be considered for further investigations by means of thrombophilic screening, Doppler ultrasound evaluation, and in the presence of portal hypertension, endoscopy and liver biopsy.